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Hriirhani Vomits Inivcrsity 
Harold B. Lee Lihrarv 



, ROLD B. LEE LIBRARY 

[4hAM YOUNG UNWERSITV 

PROVO, UTAH 




Gift of 
Tanya Kirwan 



s>. 



^•^ 






Digitized by the Internet Archive 
in 2011 with funding from 
Brigham Young University 



http://www.archive.org/details/anatomyofhumanbo1918gray 



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I 



: 7 



ANATOMY 



OF 



THE HUMAN BODY 



:by 
HENRY GRAY, F.R.S. 

FELLOW OF THE ROYAL COLLEGE OF SURGEONS; LECTURER ON ANATOMY AT ST. GEORGE's 

HOSPITAL MEDICAL SCHOOL, LONDON 



TWENTIETH EDITION 

THOROUGHLY REVISED AND RE-EDITED 

BY 
WARREN H. LEWIS, B.S., M.D. 

PROFESSOR OF PHYSIOLOGICAL ANATOMY, JOHNS HOPKINS UNIVERSITY, BALTIMORE, MD. 



HUustratet) mth 1247 jenoravtngs 




LEA & FEBIGER 
PHILADELPHIA AND NEW YORK 



Copyright 
LEA & FEBIGER 
1918 



^r"^"-^?" 



PROVO, UTAH 



THE FIRST EDITION OF THIS WORK 



WAS DEDICATED TO 



SIR BENJAMIN COLLINS BRODIE, Bart., F.R.S., D.C.L. 

IN ADMIRATION OF 

HIS GREAT TALENTS 

AND IX REMEMBRANCE OF 

MANY ACTS OF KINDNESS SHOWN TO THE ORIGINAL 

AUTHOR OF THE BOOK 

FROM AN 

EARLY PERIOD OF HIS PROFESSIONAL CAREER 



PREFACE TO THE TWENTIETH EDITION. 



SixcE the publication of the first English edition of this work in 1858 and the 
first American edition in 1859 great advances in the subject of Anatomy have been 
made, especially in microscopic anatomy and the anatomy of the embrjo. This 
knowledge was embodied from time to time in the successive editions until finally 
considerable portions of the text, sometimes sections, were devoted to these sub- 
jects. However, the main text has always remained primarily a descriptive 
anatomy of the human body. 

In the present edition the special sections on embryology and histology have 
been distributed among the subjects under which they naturally belong. New 
matter on physiological anatomy, laws of bone architecture, the mechanics and 
variations of muscles have been added, occupying much of the space formerly 
devoted to the sections pn applied anatomy. 

The sections on the ductless glands and the nervous system have been largely 
rewritten. In the latter a more rational presentation of the sympathetic nervous 
system has been achieved through the use of diagrams and descriptions based on 
physiological and pharmacological work. The central connections of the spinal 
and cranial nerves are also emphasized. 

Illustrations have been added wherever important points could be made more 
clear, and throughout the work colored pictures have been even more extensively 
used than heretofore. In this respect special mention might be made of the central 
nervous system and the section on the muscles. In the section on Syndesmology 
six illustrations are used from Quain's Anatomy through the courtesy of the 
publishers, Messrs. Longmans, Green & Company, of London. 

The use of the B. N. A. nomenclature in English has been retained practically 
unchanged in this edition and important references to the literature have been 
added at the end of each section. 

As a practical work on the subject for the student, Gray's Anatomy has always 
been recognized and appreciated. The plan originally formulated, which has 
proved so successful, has been adhered to as much as possible. It is interesting to 
note that although Henry Gray saw only the first edition, much of the original 
text persists and many of his illustrations are still in use. Bearing this in mind it 
has been the endeavor of the Editor to supply only such changes as advances in 
the science made necessarv in order that this work may reflect the latest accessions 

to anatomical knowledge. 

W. H. L. 

Baltimore, 1918. 



CONTENTS. 



EMBRYOLOGY. 



The Animal Cell. 



Cytoplasm 35 

Nucleus 36 

Reproduction of Cells 36 

Prophase 36 

Metaphase 36 

Anaphase ... 36 

Telophase ... . . 38 

The Ovum. 



Yolk 

Germinal Vesicle 
Coverings of the Ovum 
Maturation of the Ovum 



The Spermatozoon . 
Fertilization of the Ovum 
Segmentation of the Fertilized Ovum. 



The Neural Groove and Tube 
The Notochord . 



39 
40 
40 
40 

42 

44 



The Primitive Streak; Formation of the 

Mesoderm 47 

Ectoderm 47 

Entoderm 49 

Mesoderm 49 



50 
52 



The Primitive Segments 
Separation of the Embryo 
The Yolk-sac . 



52 
53 
54 



Development of the Fetal Membranes and Placenta. 

The Allantois 54 

The Amnion 56 

The Umbilical Cord and Body-stalk ... 57 

Implantation or Imbedding of the Ovum . 58 

The Decidua 59 

The Chorion 60 

The Placenta 62 

Fetal Portion 62 

Maternal Portion 63 

Separation of the Placenta .... 64 



The Branchial Region. 

The Branchial or Visceral Arches and Pharyn- 
geal Pouches 65 

The Nose and Face 67 

The Limbs 71 

Development of the Body Cavities . . 72 

The Form of the Embryo at Different Stages 

of its Growth . ... 74 



OSTEOLOGY. 



Long Bones . 79 

Short Bones 79 

Flat Bones 79 

Irregular Bones 80 

Surfaces of Bones 80 

Development of the Skeleton. 

The Skeleton 80 

The Vertebral Column 80 

The Ribs 82 

The Sternum 83 

The Skull 83 

Bone. 

Structure and Physical Properties ... 86 

Periosteum 87 

Marrow 87 

Vessels and Nerves of Bone 88 

Minute Anatomy 89 

Chemical Composition 91 

Ossification 91 

Intramembranous Ossification ... 91 

Intercartilaginous Ossification ... 93 

The Vertebral Column. 



General Characteristics of a Vertebra. 



The Cervical Vertebrae 

The First Cervical Vertebra . 
The Second Cervical Vertebra 
The Seventh Cervical Vertebra 



97 

99 

100 

101 



The Thoracic Vertebra 

The First Thoracic Vertebra 
The Ninth Thoracic Vertebra 
The Tenth Thoracic Vertebra 
The Eleventh Thoracic Vertebra 
The Twelfth Thoracic Vertebra 

The Lumbar Vertebrae 

The Fifth Lumbar Vertebra . 

The Sacral and Coccygeal Vertebrae 
The Sacrum ..... 
The Coccyx 

Ossification of the Vertebral Column 



The Vertebral Column as a Whole. 



102 
104 
104 
104 
104 
104 
104 
106 
106 
106 
111 
111 



Curves 114 

Surfaces 114 

Vertebral Canal . . 116 

The Thor.\x. 

Boundaries 117 

The Sternum 119 

Manubrium 120 

Body 120 

Xiphoid Process 121 

The Ribs 123 

Common Characteristics of the Ribs . 123 

Peculiar Ribs 125 

First Rib 125 

Second Rib 125 

Tenth Rib 126 

Eleventh and Twelfth Ribs . . 126 

The Costal Cartilages 127 

(9) 



10 



CONTENTS 



The Skull. 
The Cranial Bones. 

The Occipital Bone 129 

The Squama 129 

Lateral Parts 131 

Basilar Parts 132 

Angles 132 

The Parietal Bone 133 

The Frontal Bone 135 

Squama 135 

Orbital or Horizontal Part .... 137 

The Temporal Bone 138 

The Squama 139 

Mastoid Portion 141 

Petrous Portion 142 

Tympanic Part 145 

Styloid Process 145 

The Sphenoid Bone 147 

Body 147 

The Great Wings 149 

The Small Wings 151 

Pterygoid Processes 151 

The Sphenoidal Conchse 152 

Ethmoid bone 153 

Cribriform plate 153 

Perpendicular Plate 154 

Labyrinth or Lateral Mass .... 154 

Sutural or Wormian Bones 156 



The Facial Bones. 

The Nasal Bones 156 

The Maxillae (Upper Jaw) . • . . . 157 
The Maxillary Sinus or Antrum of High- 
more 160 

The Zygomatic Process 161 

The Frontal Process 161 

The Alveolar Process 161 

The Palatine Process 162 

Changes Produced in the Maxilla by Age 163 

The Lacrimal Bone 163 

The Zygomatic Bone 164 

The Palatine Bone 166 

The Horizontal Part 167 

The Vertical Part 167 

The Pyramidal Process or Tuberosity . 168 

The Orbital Process 168 

The Sphenoidal Process 169 

The Inferior Nasal Concha 169 

The Vomer 170 

The Mandible (Lower Jaw) 172 

Changes Produced in the Mandible by 

Age 175 

The Hyoid Bone 177 



The Exterior of the Skull. 

Norma Verticalis 178 

Norma Basalis 179 

Norma Lateralis 182 

The Temporal Fossa 183 

The Infratemporal Fossa .... 184 

The Pterygopalatine Fossa .... 185 

Norma Occipitalis 185 

Norma Frontalis 185 

The Orbits 188 



The Interior of the Skull. 

Inner Surface of the Skull-cap .... 189 

Under Surface of the Base of the Skull . 190 

The Anterior Fossa 190 

The Middle Fossa 190 

The Posterior Fossa 192 

The Nasal Cavity 194 

Anterior Nasal Aperture 196 

Dififerences in the Skull Due to Age . . . 196 

Sexual Differences in the Skull .... 197 

Craniology 197 



The Extremities. 

The Bones of the Upper -Extremity. 

The Clavicle 200 

Lateral Third 200 

Medial Two-thirds 201 

The Sternal Extremity 202 

The Acromial Extremity 202 

The Scapula 202 

The Spine 203 

The Acromion 203 

The Coracoid Process 207 

The Humerus 209 

Upper Extremity 209 

The Head 209 

The Anatomical Neck .... 209 

The Greater Tubercle .... 209 

The Lesser Tubercle .... 209 

The Body or Shaft 209 

The Lower Extremity 212 

The Ulna 214 

The Upper Extremity 214 

The Olecranon 214 

The Coronoid Process .... 214 

The Semilunar Notch .... 215 

The Radial Notch 215 

The Body or Shaft 215 

The Lower Extremity 218 

The Radius 219 

The Upper Extremity 219 

The Body or Shaft 219 

The Lower Extremity 220 

The Hand. 

The Carpus 221 

Common Characteristics of the Carpal 

Bones 221 

Bones of the Proximal Row . . . .221 
The Na\acular Bone . . . .221 

The Lunate Bone 224 

The Triangular Bone .... 224 

The Pisiform Bone 225 

Bones of the Distal Row .... 225 

The Greater Multangular Bone . 225 

The Lesser Multangular Bone . 225 

The Capitate Bone 226 

The Hamate Bone 227 

The Metacarpus 227 

Common Characteristics of the Meta- 
carpal Bones . . . . . . . 227 

Characteristics of the Individual Meta- 
carpal Bones 228 

The First Metacarpal Bone . . 228 

The Second Metacarpal Bone . . 228 

The Third Metacarpal Bone . . 228 

The Fourth Metacarpal Bone . . 228 

The Fifth Metacarpal Bone . . 228 

The Phalanges of the Hand 230 

Ossification of the Bones of the Hand . 230 

The Bones of the Lower Extremity. 

The Hip Bone 231 

The Ilium 231 

The Body 231 

The Ala 232 

The Ischium 234 

The Body 234 

The Superior Ramus .... 235 

The Inferior Ramus 235 

The Pubis 236 

The Body 236 

The Superior Ramus .... 236 

The Inferior Ramus 237 

The Acetabulum 237 

The Obturator Foramen . . . 237 

The Pelvis 238 

The Greater or False Pelvis .... 238 

The Lesser or True Pelvis .... 239 

Axes ... 240 

Position of the Pelvis 241 

Differences between Male and Female 

Pelves 241 

Abnormalities 242 



CONTENTS 



11 



The Femur 242 

The Upper Extremity 243 

The Head 243 

The Neck 243 

The Trochanters 244 

The Body or Shaft 246 

The Lower Extremity 247 

The Architecture of the Femur . . . 248 

The Patella 255 

The Tibia 256 

The Upper Extremity 256 

The Body or Shaft 257 

The Lower Extremity 259 

The Fibula 260 

The Upper Extremity or Head . . . 260 

The Body or Shaft 260 

The Lower Extremity or Lateral 

Malleolus 262 

The Fool. 

The Tarsus 263 

The Calcaneus 263 



The Tarsus— 

The Talus 266 

The Cuboid Bone 269 

The Navicular Bone 270 

The First Cuneiform Bone .... 270 
The Second Cuneiform Bone . . .271 

The Third Cuneiform Bone .... 271 

The Metatarsus 272 

Common Characteristics of the Meta- 
tarsal Bones 272 

Characteristics of the Individual Meta- 
tarsal Bones 272 

The First Metatarsal Bone ... 272 

The Second Metatarsal Bone . . 273 

The Third Metatarsal Bone . . 274 

The Fourth Metatarsal Bone . ' . 274 

The Fifth Metatarsal Bone . . 274 

The Phalanges of the Foot 275 

Ossification of the Bones of the Foot . . 275 
Comparison of the Bones of the Hand and 

Foot 276 

The Sesamoid Bones 277 



SYNDESMOLOGY. 



Bone 279 

Hyaline Cartilage 279 

Articular Cartilage 280 

Costal Cartilage 281 

White Fibrocartilage 281 

Interarticular FibrocartUages . . . 281 

Connecting FibrocartUages .... 282 

Circumferential FibrocartUages . . . 282 

Stratiform Fibrocartilages .... 282 

Ligaments 282 

The Articular Capsules 282 

Mucous Sheaths 283 

BursjE Mucosae 283 

Development of the Joints . . 283 



Classification of Joints 

Synarthrosis 284 

Sutura 284 

Schindylesis 284 

Gomphosis 284 

Synchondrosis 284 

Amphlarthrosis 285 

Diathrosis 285 

Ginglimus • 285 

Trochoid 285 

Condyloid 286 

Articulation by Reciprocal Reception . 286 

Enarthrosis 286 

Arthrodia 286 



The Kind of Movement Admitted in Joints. 

Gliding Movement 286 

Angular Movement 286 

Circumduction 286 

Rotation 287 

Ligamentous Action of Muscles .... 287 



Articulations of the Trunk. 

Articulations of the Vertebral Column . . 287 
Articulations of Vertebral Bodies . . 287 
The Anterior Longitudinal Liga- 
ment 287 

The Posterior Longitudinal Liga- 
ment 288 

The Intervertebral Fibrocartilages 289 

Structure 289 

Articulations of Vertebral Arches . . 289 

The Articular Capsules .... 290 

The Ligamenta Flava .... 290 

The Supraspinal Ligament . . . 290 



Articulations of the Vertebral Column — 
Articulations of Vertebral Arches — 

The Ligamentum Nuchce . . . 290 
The Interspinal Ligaments . . . 291 
The Intertransverse Ligaments . 291 
Articulation of the Atlas with the Epistro- 
pheus or Axis 292 

The Articular Capsules 292 

The Anterior Atlantoaxial Ligament . 293 

The Posterior Atlantoaxial Ligament . 293 

The Transverse Ligament of the Atlas . 293 
Articulations of the Vertebral Column with 

the Cranium 295 

Articulation of the Atlas with the 

Occipital Bone 295 

The Articular Capsules .... 295 
The Anterior Atlantooccipital Mem- 
brane 295 

The Posterior Atlantooccipital Mem- 
brane 296 

The Lateral Ligaments .... 296 
Ligaments Connecting the Axis with the 

Occipital Bone 296 

The Membrana Tectoria . . . 296 

The Alar Ligaments 296 

Articulation of the Mandible 297 

The Articular Capsule 297 

The Temporomandibular Ligament . 297 

The Sphenomandibular Ligament . . 297 

The Articular Disk 298 

The Stylomandibular Ligament . . . 298 

Costovertebral Articulations 299 

Articulations of the Heads, of the Ribs . 299 
The Articular Capsule .... 299 
The Radiate Ligament .... 299 
The Interarticular Ligament . . 300 
Costotransverse Articulations . . . 300 
The Articular Capsule .... 301 
The Anterior Costotransverse Liga- 
ment 301 

The Posterior Costotransverse Liga- 
ment 301 

The Ligament of the Neck of the 

Rib 302 

The Ligament of the Tubercle of 

the Rib 302 

Sternocostal Articulations 302 

The Articular Capsules 302 

The Radiate Sternocostal Ligaments . 302 
The Interarticular Sternocostal Liga- 
ment 303 

The Costoxiphoid Ligaments . . . 304 

Interchondral Articulations .... 304 

Costochondral Articulations .... 304 
Articulation of the Manubrium and Body of 

the Sternum 304 

Mechanism of the Thorax .... 304 



12 



CONTENTS 



Articulation of the Vertebral Column with 

the Pelvis 306 

The Iliolumbar Ligament .... 306 

Articulations of the Pelvis 306 

Sacroiliac Articulation 306 

The Anterior Sacroiliac Ligament . 307 
The Posterior Sacroiliac Ligament. 307 
The Interosseous Sacroiliac Liga- 
ment 308 

Ligaments Connecting the Sacrum and 

Ischium 309 

The Sacrotuberous Ligament . 309 
The Sacrospinous Ligament . . 309 
Sacrococcygeal Symphysis .... 309 
The Anterior Sacrococcygeal Liga- 
ment .309 

The Posterior Sacrococcygeal Liga- 
ment 309 

The Lateral Sacrococcygeal Liga- 
ment 310 

The Interarticular Ligaments . 310 

The Pubic Symphysis 310 

The Anterior Pubic Ligament . . 310 

The Posterior Pubic Ligament . . 310 

The Superior Pubic Ligament . . 310 

The Arcuate Pubic Ligament . . 310 
The Interpubic Fribrocartilaginous 

Lamina 311 

Mechanism of the Pelvis 311 



Articulations of the Upper Extremity. 

Sternoclavicular Articulation 313 

The Articular Capsule 313 

The Anterior Sternoclavicular Ligament 313 
The Posterior Sternoclavicular Liga- 
ment 313 

The Interclavicular Ligament . . . 314 

The Costoclavicular Ligament . . 314 

The Articular Disk 314 

Acromioclavicular Articulation .... 315 

The Articular Capsule 315 

The Superior Acromioclavicular Liga- 
ment . . 315 

The Inferior Acromioclavicular Liga- 
ment 315 

The Articular Disk 315 

The Coracoclavdcular Ligament . . .315 

The Trapezoid Ligament .... 315 

The Conoid Ligament 315 

The Ligaments of the Scapula . . . . 316 

The Coracoacromial Ligament . . . 316 

The Superior Transverse Ligament . . 317 

The Inferior Transverse Ligament . . 317 

Humeral Articulation or Shoulder-joint . . 317 

The Articular Capsule 317 

The Coracohumeral Ligament . . . 318 
Glenohumeral Ligaments . . . .318 

The Transverse Humeral Ligament . 319 

The Glenoidal Labrum 319 

Bursse 319 

Elbow-joint 321 

The Anterior Ligament 321 

The Posterior Ligament 322 

The Ulnar Collateral Ligament . . . 322 

The Radial Collateral Ligament . . 322 

Radioulnar Articulation 324 

Proximal Radioulnar Articulation . . 324 

The Annular Ligament .... 324 

Middle Radioulnar Union .... 325 

The Oblique Cord 325 

The Interosseous Membrane . . 325 

Distal Radioulnar Articulation . . . 325 

The Volar Radioulnar Ligament 325 

The Dorsal Radioulnar Ligament . 325 

The Articular Disk 325 

Radiocarpal Articulation or Wrist- joint . . 327 

The Volar Radiocarpal Ligament . . 327 

The Dorsal Radiocarpal Ligament . . 328 

The Ulnar Collateral Ligament . . . 328 

The Radial Collateral Ligament . . 328 

Intercarpal Articulations 328 

Articulations of the Proximal Row of 

Carpal Bones 328 



Intercarpal Articulations — 

Articulations of the Proximal Row of 
Carpa Bones — 
The Dorsal Ligaments .... 328 
The Volar Ligaments .... 328 
The Interosseous Ligaments . . 328 
Articulations of the Distal Row of 

Carpal Bones 329 

The Dorsal Ligaments .... 329 
The Volar Ligaments .... 329 
The Interosseous Ligaments . . 329 
Articulations of the Two Rows of 
Carpal Bones with Each Other . 
The Volar Ligaments .... 
The Dorsal Ligaments . ' . . 
The Collateral Ligaments . 
Carpometacarpal Articulations .... 
Carpometacarpal Articulation of the 

Thumb 330 

Articulations of the Other Four Meta- 
carpal Bones with the Carpus 
The Dorsal Ligaments . 
The Volar Ligaments 
The Interosseous Ligaments 
Intermetacarpal Articulations 

The Transverse Metacarpal Ligament 
Metacarpophalangeal Articulations . 

The Volar Ligaments 332 

The Collateral Ligaments , . . . . 332 
Articulations of the Digits 333 



329 
329 
329 
329 
330 



331 
331 
331 
331 
331 
331 
332 



Articulations of the Lower Extremity. 



Coxal Articulation or Hip- joint . 

The Articular Capsule .... 
The Iliofemoral Ligament 
The Pubocapsular Ligament 
The Ischiocapsular Ligament 
The Ligamentum Teres Femoris 
The Glenoidal Labrum .... 
The Transverse Acetabular Ligament 

The Knee-joint 

The Articular Capsule .... 
The Ligamentum Patellae 
The Oblique Popliteal Ligament 
The Tibial Collateral Ligament . 
The Fibular Collateral Ligament 
The Cruciate Ligaments .... 

The Anterior Cruciate Ligament 

The Posterior Cruciate Ligament 
The Menisci 

The Medial Meniscus 

The Lateral Meniscus 
The Transverse Ligament 
The Coronarj' Ligaments 

Bursse 

Articulations between the Tibia and 
Tibiofibular Articulation 

The Articular Capsule . 

The Anterior Ligament . 

The Posterior Ligament 
Interosseous Membrane . 
Tibiofibular Syndesmosis 

The Anterior Ligament . 

The Posterior Ligament 

The Inferior Transverse Ligament 

The Interosseous Ligament 
Talocrural Articulation or Ankle-joint 
The Articular Capsule .... 
The Deltoid Ligament .... 
The Anterior Talofibular Ligament 
The Posterior Talofibular Ligament 
The Calcaneofibular Ligament . 

Intertarsal Articulations 

Talocalcaneal Articulation 

The Articular Capsule . 

The Anterior Talocalcaneal Liga 
ment 

The Posterior Talocalcaneal Liga 
ment 

The Lateral Talocalcaneal Liga 
ment 

The Medial Talocalcaneal Liga 
ment 




333 
334 
335 
335 
335 
336 
336 
336 
339 
340 
340 
340 
341 
341 
342 
342 
342 
342 
343 
343 
343 
343 
345 
347 
348 
348 
348 
348 
348 
348 
348 
348 
349 
349 
349 
350 
350 
351 
351 
351 
352 
352 
352 

352 

352 

352 

353 



CONTENTS 



13 



Intertarsal Articulations — 

Talocalcaneal Articulation — 

The Interosseous Talocalcaneal 

Ligament 

Talocalcaneonavicular Articulation . 
The Articular Capsule . 
The Dorsal Talonavicular Ligament 
Calcaneocuboid Articulation 
The Articular Capsule . 
TheDorsalCalcaneocuboidLigamen 
The Bifurcated Ligament . 
The Long Plantar Ligament 
The Plantar Calcaneocuboid Liga 

ment 

The Ligaments Connecting the Galea 
neus and Navicular 
The Plantar Calcaneonavicular 

Ligament 

Cuneonavicular Articulation 
The Dorsal Ligaments . 
The Plantar Ligaments . 
Cuboideonavicular Articulation . 
The Dorsal Ligament 



353 
353 
354 
354 
354 
354 
354 
354 
354 

354 

355 

355 
356 
356 
356 
356 
357 



Intertarsal Articulations — 

Cuboideonavicular Articulation — 

The Plantar Ligament .... 357 
The Interosseous Ligament . . 357 
Intercuneiform and Cuneocuboid Articu- 
lation 357 

The Dorsal Ligaments .... 357 

The Plantar Ligaments .... 357 

The Interosseous Ligaments . . 357 

Tarsometatarsal Articulations .... 358 

The Dorsal Ligaments 358 

The Plantar Ligaments 358 

The Interosseous Ligaments .... 358 

Intermetatarsal Articulations 358 

The Dorsal Ligaments 358 

The Plantar Ligaments 358 

The Interosseous Ligaments .... 358 

The Transverse Metatarsal Ligament . 359 

Metatarsophalangeal Articulations . . . 359 

The Plantar Ligaments 359 

The Collateral Ligaments .... 359 

Articulations of the Digits 359 

Arches of the Foot 360 



MYOLOGY. 



Mechanics of Muscle. 

The Direction of Muscle Pull 
The Action of Muscle Pull on Tendon 
The Strength of Muscles .... 
The Work Accomplished by Muscles 
The Action of Muscles on Joints 



Development of the Muscles. 

The Ventro-lateral Muscles of the Neck . 
Muscles of the Shoulder Girdle and Arm 

The Muscles of the Leg 

The Muscles of the Head 

Striped or Voluntary Muscle .... 
Vessels and Nerves of Striped Muscle 



363 
364 
364 
365 
368 



371 
371 
372 
372 
373 
376 



Tendons, Aponeuroses, and Fasci/e. 

Tendons 376 

Aponeuroses 376 

Fasciai 376 



The Fasci.*: and Muscles of the Head. 

The Muscles of the Scalp. 

The Skin of the Scalp 378 

The Superficial Fascia 378 

Epicranius 378 

Occipitalis 379 

Frontalis 379 

Galea Aponeurotica 380 

The Muscles of the Eyelid. 

Orbicularis Oculi 380 

Gorrugator 381 

The Muscles of the Nose. 

Procerus ... 382 

Nasalis 382 

Depressor Septi 382 

Dilator Naris Posterior ....... 382 

Dilator Naris Anterior 382 

The Muscles of the Mouth. 

Quadratus Labii Superiorio 383 

Caninus 383 

Zygomaticus 383 

Mentalis 383 



Quadratus Labii Inferioris 383 

Triangularis 383 

Buccinator 384 

Pterygomandibular Raphe .... 384 

Orbicularis Oris 384 

Risorius 385 

The Muscles of Mastication. 

Parotideomasseteric Fascia 385 

Masseter 385 

Temporal Fascia 386 

Temporalis 386 

Pterygoideus Externus 386 

Pterygoideus Internus 387 



The Fasci-e and Muscles of the Antero- 
lateral Region of the Neck. 

The Superficial Cervical Muscle. 

Superficial Fascia 387 

Platysma 388 

Variations 388 

The Lateral Cervical Muscles. 

The Fascia Colli 388 

Sternocleidomastoideus 390 

Variations 390 

Triangles of the Neck 390 

The Supra- and Infrahyoid Aluscles. 

Digastricus 391 

Variations 391 

Stylohyoideus 392 

Variations 392 

The Stylohyoid Ligament .... 392 

Mylohyoideus 393 

Variations 393 

Geniohyoideus 393 

Sternohyoideus 393 

Variations 393 

Sternothyreoideus 393 

Variations 394 

Thyreohyoideus 394 

Omohyoideus 394 

Variations 394 

The Anterior Vertebral Muscles. 

Longus Colli 394 

Longus Capitis 395 

Rectus Capitis Anterior 395 

Rectus Capitis Lateralis 395 



14 



COX TENTS 



The Lateral Vertebral Muscles. 

Scalenus Anterior 396 

Scalenus Medius 396 

Scalenus Posterior 396 

Variations 396 



The Fascia and Muscles of the Thunk. 

The Deep Muscles of the Back. 

The Lumbodorsal Fascia 397 

Splenius Capitis 397 

Splenius Cervicis 397 

Variations 397 

Sacrospinalis 397 

Iliocostalis Lumborum 399 

Iliocostalis Dorsi 399 

Iliocostalis Cervicis 399 

Longissimiis Dorsi 399 

Longissimus Cervicis 399 

Longissimus Capitis 399 

Spinalis Dorsi 399 

Spinalis Cer\-icis 400 

Spinalis Capitis 400 

Semispinalis Dorsi 400 

Semispinalis Cervicis 400 

Semispinalis Capitis 400 

Multifidus 400 

Rotatores 400 

Interspinales 400 

Extensor Coccygis 401 

Intertransversarii 401 



The Suboccipital Muscles. 



Rectus Capitis Posterior Major 
Rectus Capitis Posterior Minor 
Obliquus Capitis Inferior . 
Obliquus Capitis Superior . 
The Suboccipital Triangle 



401 
401 
402 
402 
402 



The Muscles of the Thorax. 



Intercostal Fascia 402 

Intercostales 403 

Intercostales Externi 403 

Variations 403 

Intercostales Interni 403 

Subcostales 403 

Transversus Thoracis 403 

Levatores Costarum 403 

Serratus Posterior Superior 404 

Variations 404 

Serratus Posterior Inferior 404 

Variations 404 

Diaphragm 404 

Medial Lumbocostal Arch .... 404 

Lateral Lumbocostal Arch .... 405 

The Crura 405 

The Central Tendon 406 

Openings in the Diaphragm . . . 406 

Variations 406 

Mechanism of Respiration 407 

The Muscles and Fascice of the Abdomen. 

The Antero-lateral Muscles of the Abdomen 408 

The Superficial Fascia 408 

Obliquus Externus Abdominis . 409 
Aponeurosis of the Obliquus 

Externus Abdominis . 410 
Subcutaneous Inguinal Ring . 410 
The Intercrural Fibers . 410 
The Inguinal Ligament . 411 
The Lacunar Ligament . . 412 
The Reflected Inguinal Liga- 
ment 412 

Ligament of Cooper . . . 412 

Variations 412 

Obliquus Internus Abdominis . . . 412 

Variations 414 

Cremaster 414 

Transversus Abdominis 414 



The Antero-lateral Muscles of the Abdomen — 
.Transversus Abdominis — 

Variations 414 

Inguinal Aponeurotic Falx . . . 414 

Rectus Abdominis 415 

Pyramidalis 416 

Variations 417 

The Linea Alba 417 

The Linese Semilunares 417 

The Transversalis Fascia .... 418 

The Abdominal Inguinal Ring . . . 418 

The Inguinal Canal 418 

Extraperitoneal Connective Tissue . . 418 

The Deep Crural Arch 419 

The Posterior Muscles of the Abdomen . . 419 
The Fascia Covering the Quadratus 

Lumborum 419 

Quadratus Lumborum 420 

Variations 420 

The Muscles and Fascia of the Pelvis. 

Pehac Fascia 420 

Levator Ani 422 

Coccygeus 424 

The Muscles and Fascia of the Perineum. 

Muscles of the Anal Region 424 

The Superficial Fascia 424 

The Deep Fascia 425 

Ischiorectal Fossa 425 

The Corrugator Cutis Ani .... 425 

Sphincter Ani Externus 425 

Sphincter Ani Internus 426 

The ^Iuscles of the Urogenital Region in 

the Male 426 

Superficial Fascia 426 

The Central Tendinous Point of the 

Perineum 427 

Transversus Perinsei Superficialis . . 427 

Variations 427 

Bulbocavernosus 42S 

Ischiocavernosus 428 

The Deep Fascia . . . . . . .428 

Transversus Perinsei Profundus . . 429 

Sphincter L'rethrae Membranace® . . 429 

The Muscles of the L'rogenital Region in the 

Female 430 

Transversus Perinoei Superficialis . . 43o 

Bulbocavernosus 430 

Ischiocavernosus 430 

Transversus Perinsei Profundus . . 431 



The Fascia axd Muscles of the Upper 
Extremity. 

The Muscles Connecting the Upper Extremity 
to the Vertebral Column. 

Superficial Fascia 432 

Deep Fascia 432 

Trapezius 432 

\'ariations 432 

Latissimus Dorsi 432 

Variations 434 

Rhomboideus Major 434 

Rhomboideus Minor 434 

Variations 435 

Levator scapulae 435 

Variations 435 

The Muscles Connecting the Upper Extremity to 
the Anterior and Lateral Thoracic Walls. 

Superficial Fascia 435 

Pectoralis Major 436 

Variations 437 

Coracoclavicular Fascia 437 

Pectoralis Minor 438 

Variations 438 

Subcla\-ius 438 

^'ariations 438 

Serratus Anterior '. 438 

\'ariations 439 



CONTENTS 



15 



The Muscles and Fascia of the Shoulder. 

Deep Fascia 439 

Deltoideus 439 

Variations 440 

Subscapular Fascia 440 

Subscapularis 440 

Supraspinatous Fascia 440 

Supraspinatus 440 

Infraspinatous Fascia 441 

Infraspinatus 441 

Teres Minor 441 

Variations 442 

Teres Major 442 

The Muscles and Fasciae of the Arm. 

Brachial Fascia 442 

Coracobrachialis . 443 

Variations 443 

Biceps Brachii 443 

Variations 444 

Brachialis 444 

Variations 444 

Triceps Brachii 444 

Variations 445 

The Muscles and Fasciae of the Forearm. 

Antibrachial Fascia 445 

The Volar Antibrachial Muscles .... 445 

The Superficial Group 446 

Pronator Teres 446 

Variations 446 

Flexor Carpi Radialis .... 446 

Variations 446 

Palmaris Longus . . . . . . 446 

Variations 446 

Flexor Carpi Ulnaris .... 447 

Variations 447 

Flexor Digitorum Sublimis . . . 448 

Variations 448 

The Deep Group 448 

Flexor Digitorum Profundus . 448 
Fibrous Sheaths of the Flexor 

Tendons 448 

Variations 449 

Flexor PoUicis Longus .... 449 

Variations 449 

Pronator Quadratus . . . . . 449 

Variations 450 

The Dorsal Antibrachial Muscles. . . .451 

The Superficial Group 451 

Brachioradialis 451 

Variations 451 

Extensor Carpi Radialis Longus . 452 

Extensor Carpi Radialis Brevis . 452 

Variations 452 

Extensor Digitorum Communis . 452 

Variations 454 

Extensor Digiti Quinti Proprius . 454 

Variations 454 

Extensor Carpi L^lnaris .... 454 

Variations 454 

AnconiBUS 454 

The Deep Group 454 

Supinator 454 

Abductor PoUicis Longus . . . 455 

Variations 455 

Extensor PoUicis Brevis . . . 455 

Variations 455 

Extensor PoUicis Longus . . . 455 

Extensor Indicis Proprius . . . 456 

Variations 456 

Thii Muscles and Fascia: of the Hand. 

Volar Carpal Ligament 456 

Transverse Carpal Ligament 456 

The Mucous Sheaths of the Tendons on the 

Front of the Wrist 457 

Dorsal Carpal Ligament 458 

The Mucous Sheaths of the Tendons on the 

Back of the Wrist 459 

Palmar Aponeurosis 460 



Superficial Transverse Ligament of the 

Fingers 461 

The Lateral Volar Muscles 461 

Abductor PoUicis Brevis 461 

Opponens PoUicis 461 

Flexor PoUicis Brevis 461 

Adductor PoUicis (Obliquus) . . . 462 

Adductor PoUicis (Transversus) . . 462 

Variations 462 

The Medial Volar Muscles 462 

Palmaris Brevis 463 

Abductor Digiti Quinti 463 

Flexor Digiti Quinti Brevis .... 464 

Opponens Digiti Quinti 464 

Variations 464 

The Intermediate Muscles 464 

Lumbricales 464 

Variations 464 

Interossei 464 

Interossei Dorsales 464 

Interossei Volares 465 



The Muscles and Fasciae of the Lower 
Extremity. 

The Muscles and Fasciae of the Iliac Region. 

The Fascia Covering the Psoas and Iliacus 466 

Psoas Major 467 

Psoas Minor 467 

Iliacus 467 

Variations 467 

The Muscles and Fasciae of the Thigh. 

The Anterior Femoral Muscles .... 467 

Superficial Fascia 468 

Deep Fascia 468 

The Fossa Ovalis 469 

Sartorius 470 

Variations 470 

Quadriceps Femoris 470 

Rectus Femoris 470 

Vastus Lateralis 470 

Vastus Medialis 471 

Vastus Intermedins 471 

Articularis Genu 471 

The Medial Femoral Muscles . . . .471 

Gracilis 471 

Pectineus 472 

Adductor Longus 472 

Adductor Brevis 473 

Adductor Magnus 473 

Variations 474 

The Muscles of the Gluteal Region . . . 474 

Gluteus Maximus 474 

Bursae 474 

Glutseus Medius 474 

Variations 475 

Glutseus Minimus 475 

Variations 475 

Piriformis 476 

Variations 476 

Tensor Fasciae Latte 476 

Obturator Membrane 477 

Obturator Internus 477 

Gemelli 477 

Gemellus Superior 477 

Gemellus Inferior 477 

Quadratus Femoris 477 

Obturator Externus 477 

The Posterior Femoral Muscles .... 478 

Biceps Femoris 478 

Variations 479 

Semitendinosus , 479 

Semimembranosus .... . 479 

Variations .... . . 479 

The Muscles and Fasciae of the Leg. 

The Anterior Crural Muscles 480 

Deep Fascia 480 

Tibialis Anterior 480 

Variations 480 



16 



CONTEXTS 



The Anterior Crural Muscles — 

Extensor Hallucis Longus .... 481 

\"ariations 481 

Extensor Digitorum Longus .... 481 

\'ariation3 482 

Peronspus Tertius 482 

The Posterior Crural Muscles . . . 482 

The Superficial Group 482 

Gastrocnemius 482 

\'ariatioiis 483 

Soleus 483 

Variations 483 

Tendo Calcaneus 483 

Plantaris 483 

The Deep Group ....... 483 

Deep Transverse Fascia . . . 483 

Popliteus 484 

Variations 485 

Flexor Hallucis Longus .... 485 

Variations 485 

Flexor Digitorum Longus . . 485 

Variations 485 

Tibialis Posterior 485 

The Lateral Crural Muscles 486 

Peron;rus Longus 486 

Peronajus Brevis 486 

Variations 487 

The FascicB Around the Ankle. 

Transverse Crural Ligament ..... 488 

Cruciate Crural Ligament 488 

Laciniate Ligament , 489 

Peroneal Retinacula 489 



The Mucous Sheaths of the Tendons Around 
the Ankle 

The Muscles and Fasciae of the Foot. 



489 



The Dorsal Muscle of the Foot .... 490 

Extensor Digitorum Brevis .... 490 

^'ariations 490 

The Plantar Muscles of the Foot . . . 490 

Plantar Aponeurosis 490 

The First Layer 491 

Abductor Hallucis 491 

Variations 491 

Flexor Digitorum Brevis . . .491 

Variations 492 

Fibrous Sheaths of the Flexor 

Tendons 492 

Abductor Digiti Quinti .... 492 

Variations 492 

The Second Layer 493 

Quadratus PlantiB 493 

Variations 493 

Lumbricales 493 

Variations 493 

The Third Layer 493 

Flexor Hallucis Bre^ns .... 493 

Variations 493 

Adductor Hallucis 493 

Variations 494 

Flexor Digiti Quinti Bre^•is . . 494 

The Fourth Layer 495 

Interossei 495 

Interossei Dorsales .... 495 

Interossei Plantares . . . 495 



ANGIOLOGY. 



Structure of Arteries 498 | The Thoracic Cavitt. 

Capillaries 499 

Sinusoids 501 The Cavity of the Thorax . . . 

Structure of Veins 591 The Upper Opening of the Thorax 

The Lower Opening of the Thorax 



524 
524 
524 



The Blood. 

General Composition of the Blood . . . 503 

Blood Corpuscles 503 

Colored or Red Corpuscles . . . 503 

Colorfesg Corpuscles or Leukocytes 504 



Development of the Vascular System. 

Further Development of the Heart . . . 508 

The Valves of the Heart 514 

Further Development of the Arteries . 515 
The Anterior Ventral Aortae . . .516 

The Aortic Arches 516 

The Dorsal Aortae 517 

Further Development of the Veins . . 518 

The Visceral Veins 518 

The Parietal Veins 520 

Inferior Vena Cava 520 

Venous Sinuses of the Dura Mater . 522 



The Pericardium. 

Structure of the Pericardium 525 

The Heart. 

Size 526 

Component Parts 526 

Right Atrium 528 

Sinus Venarum 528 

Auricula 528 

Right Ventricle 531 

Left Atrium 533 

Auricula 533 

Left Ventricle 535 

V^entricular Septum 535 

Structure of the Heart 535 

The Cardiac Cycle and the Actions of the 

Valves 538 

Peculiarities in the Vascular System in the 
Fetus. 

Fetal Circulation 540 

Changes in the Vascular System at Birth . 542 



THE ARTERIES. 



The Pulmonary Arterj" 
Relations 



543 
545 



The Aorta. 
The Ascending Aorta. 



Relations 
Branches 



546 
546 



Branches of the Ascending Aorta — 

The Coronarj' Arteries 546 

Right Coronarj' Arterj- .... 546 

Left Coronarj- Artery .... 547 

Pecuharities 547 

The Arch of the Aorta. 

Relations 547 

Peculiarities 548 



CONTENTS 



17 



Branches 548 

Peculiarities ' 548 

The Innominate Artery , 548 

Relations 548 

Branches 549 

ThjTeoidea Ima 549 

Collateral Circulation 549 



The Arteries of the Head and Neck. 



The Common Carotid Artery. 

Relations 549 

Peculiarities 551 

Collateral Circulation 551 

The External Carotid Artery 551 

Relations 552 

Branches 552 

Superior Thyroid Artery . . . 552 

Relations 552 

Branches 552 

Lingual Artery 553 

Relations 553 

Branches 553 

External Maxillary Artery . . . 553 

Relations 554 

Branches 554 

Peculiarities 556 

Occipital Artery 556 

Course and Relations . . 556 

Branches 556 

Posterior Auricular Artery . . . 557 

Branches 557 

Ascending Pharyngeal Artery . . 557 

Branches 558 

Superficial Temporal Artery . . 558 

Relations 558 

Branches 558 

Internal Maxillary Artery . . . 559 

Branches 560 

The Triangles of the Neck 562 

Anterior Triangle 563 

Inferior Carotid or Muscular Tri- 
angle 563 

Superior Carotid or Carotid Tri- 
angle 564 

Submaxillary or Digastric Tri- 
angle 564 

Suprahyoid Triangle .... 565 

Posterior Triangle 565 

Occipital Triangle 565 

Subclavian Triangle 565 

The Internal Carotid Artery 566 

Course and Relations 567 

Cer\ical Portion 567 

Petrous Portion 567 

Cavernous Portion 567 

Cerebral Portion . 567 

Peculiarities 567 

Branches 568 

Caroticotympanic 568 

Artery of the Pterygoid Canal . . 568 

Cavernous 568 

Hypophyseal 568 

Semilunar 568 

Anterior Meningeal 568 

Ophthalmic artery 568 

Branches 568 

Anterior Cerebral Artery . . . 571 

Branches 571 

Middle Cerebral Artery . . . 572 

Branches 573 

Posterior Communicating Artery . 573 

Anterior Choroidal Artery . . . 574 



The Arteries of the Brain. 



The Ganglionic System 

The Cortical Arterial System 



575 
575 



The Arteries of the Upper Extremity. 

The Subclavian Artery. 

First Part of the Right Subclavian Artery . 576 

Relations 576 

First Part of the Left Subclavian Artery . 577 

Relations 577 

Second and Third Parts of the Subclavian 

Artery 577 

Relations 577 

Relations 577 

Peculiarities 577 

Collateral Circulation 578 

Branches ^78 

Vertebral Artery 578 

Relations 578 

Branches 579 

Thyrocervical Trunk 581 

Branches 581 

Peculiarities 583 

Internal Mammary Artery .... 584 

Relations 584 

Branches 584 

The Costocervical Trunk .... 585 

The Axilla. 

Boundaries 585 

Contents 586 

The Axillary Artery 586 

Relations 586 

Collateral Circulation 587 

Branches 587 

The Highest Thoracic Artery . . 587 

The Thoracoacromial Artery . 588 

The Lateral Thoracic Artery . . 588 

The Subscapular Artery . . 588 
The Posterior Humeral Circumflex 

Artery 589 

The Anterior Humeral Circumflex 

Artery 589 

Peculiarities 589 

The Brachial Artery 589 

Relations 589 

The Anticubital Fossa 589 

Peculiarities 590 

Collateral Circtilation 590 

Branches 590 

The Arteria Profunda Brachii . . 591 

The Nutrient Artery .... 591 
The Superior Ulnar Collateral 

Artery 591 

The Inferior Ulnar Collateral 

Artery 592 

Muscular Branches 592 

The Anastomosis Around the Elbow- j oint 592 

The Radial Artery 592 

Relations 592 

Peculiarities 594 

Branches 594 

Radial Recurrent Artery 594 

Muscular 594 

Volar Carpal 594 

Superficial Volar 594 

Dorsal Carpal 594 

Arteria Princeps PoUicis . . 595 

Arteria Volaris Indicis Radialis 595 

Deep Volar Arch 595 

Volar Metacarpal Arteries . . 595 

Perforating 595 

Recurrent 595 

The Ulnar Artery 595 

Relations 595 

Peculiarities 596 

Branches 596 

Anterior Ulnar Recurrent Artery . 596 

Posterior Ulnar Recurrent Artery . 596 

Common Interosseous Artery . 596 

Muscular 598 

Volar Carpal 598 

Dorsal Carpal 598 

Deep Volar 598 

Superficial Volar 598 

Relations 598 



18 



CONTENTS 



The Arteries of the Trunk. 

The Descending Aorta. 

The Thoracic Aorta 598 

Relations 599 

Peculiarities 599 

Branches 600 

Pericardial 600 

Bronchial 600 

Esophageal 600 

Mediastinal 600 

Intercostal Arteries 600 

Branches ... . 691 

Subcostal Arteries 601 

Superior Phrenic 601 

The Abdominal Aorta 602 

Relations . 603 

Collateral Circulation 603 

Branches 603 

The Celiac Artery 603 

Relations 603 

The Superior Mesenteric Artery . 606 

Branches 607 

The Inferior Mesenteric Artery . 609 

Branches 610 

The Middle Suprarenal Arteries . 610 

The Renal Arteries 610 

The Internal Spermatic Arteries . 611 
The Ovarian Arteries . . . .611 

The Inferior Phrenic Arteries . . 612 
The Lumbar Arteries . . . .612 

The Middle Sacral Artery ... 613 



The Common Iliac Arteries, 

Peculiarities 614 

Collateral CLrculatioa 614 

The Hypogastric Artery 614 

Relations 614 

Peculiarities 615 

Collateral Circulation 615 

Branches 615 

Superior Vesical Artery .... 615 

Middle Vesical Artery .... 615 

Inferior Vesical Artery . . . . 615 

Middle Hemorrhoidal Artery . . 615 

Uterine Artery 615 

Vaginal Artery 616 

Obturator Artery 616 

Branches 616 

Peculiarities 617 

Internal Pudendal Artery . . . 617 

Relations 618 

Peculiarities 618 

Branches 618 

Inferior Gluteal Artery .... 620 

Branches 620 

Lateral Sacral Arteries . . . .621 

Superior Gluteal Artery . . . 622 

The External Iliac Artery 622 

Relations 622 

Collateral Circulation 622 

Branches 622 

Inferior Epigastric Artery . . . 623 

Branches 623 

Peculiarities 623 

Deep Iliac Circumflex Artery . . 623 



The Arteries of the Lower Extremity. 

The Femoral Artery. 

The Femoral Sheath 625 

The Femoral Triangle 626 

The Adductor Canal 627 

Relations of the Femoral Artery .... 627 

Peculiarities of the Femoral Artery . . . 629 

Collateral Cii'culation 629 

Branches 629 

Superficial Epigastric Artery . . . 629 

Superficial Iliac Circumflex Artery . . 629 

Superficial External Pudendal Artery . 629 

Deep External Pudendal Artery . . 629 

Muscular 629 

Profunda Femoris Artery .... 629 

Relations 630 

Peculiarities 630 

Branches 630 

Highest Genicular Artery . . . .631 

The Popliteal Fossa 631 

Boundaries . .■ , 631 

Contents 632 

The Popliteal Artery 632 

Relations 632 

Peculiarities 633 

Branches 633 

Superior IMusculur .... 633 

Sural Arteries 633 

Cutaneous Branches . . . 633 
Superior Genicular Arteries . . 633 
Middle Genicular Artery . . 633 
Inferior Genicular Arteries . . 633 
The Anastomosis Around the Knee- 
joint 634 

The Anterior Tibial Artery 634 

Relations 635 

Peculiarities 635 

Branches 635 

Posterior Tibial Recurrent Arterj- . 635 

Fibular Artery 635 

Anterior Tibial Recurrent Artery . 635 

Muscular Branches 635 

Anterior Medial Malleolar Arterj- . 635 

Anterior Lateral Malleolar Artery . 635 

The Arteria Dorsalis Pedis 636 

Relations 636 

Peculiarities 636. 

Branches ; 637 

Lateral Tarsal Artery .... 637- 
Medial Tarsal Artery . . . .637 

Arcuate Artery 637 

Deep Plantar Artery .... 637 

The Posterior Tibial Artery 637 

Relations 637 

Peculiarities 638 

Branches 638 

Peroneal Artery 638 

Peculiarities 638 

Branches 638 

Nutrient Artery 638 

Muscular Branches 639 

Posterior Medial Malleolar Artery 639 

Communicating Branch .... 639 

Medial Calcaneal 639 

Medial Plantar Artery .... 639 

Lateral Plantar Artery .... 639 

Branches 640 



The Pulmonary Veins 
The Systemic Veins. 



The Veins of the Heart. 

Coronary Sinus 642 

Tributaries 642 

The Veins of the Head and Neck. 

The Veins of the Exterior of the Head and 

Face 644 

The Frontal Vein 644 



THE VEINS. 



642 



The Veins of the Exterior of the Head 


and 


The Supraorbital Vein 645 


The Angular Vein 






645 


The Anterior Facial Vein 






645 


Tributaries 






645 


The Superficial Temporal Vein 






645 


Tributaries .... 






645 


The Pterygoid Plexus . . 






645 


The Internal Maxillary Vein . 






646 


The Posterior Facial Vein 






646 


The Posterior Auricular Vein 






646 


The Occipital Vein 






646 



CONTENTS 



19 



The Veins of the Neck 

The External Jugular Vein 

Tributaries ... 
The Posterior External Jugular Vein 
The Anterior Jugular Vein 
The Internal Jugular Vein 

Tributaries 
The Vertebral Vein 

Tributaries 
The Diploic Veins . 
The Veins of the Brain 
The Cerebral Veins 
The External Veins 

The Superior Cerebral Vein 

The Middle Cerebral Vein . 

The Inferior Cerebral Vein . 

The Internal Cerebral Veins 

The Great Cerebral Vein 
The Cerebellar Veins .... 
The Sinuses of the Dura Mater. Ophthalmic 
Veins and Emissary Veins 
The Superior Sagittal Sinus . 
The Inferior Sagittal Sinus . 
The Straight Sinus .... 
The Transverse Sinuses . 
The Occipital Sinus .... 
The Confluence of the Sinuses . 
The Cavernous Sinuses . 
The Ophthalmic Veins 

The Superior Ophthalmic Vein 

The Inferior Ophthalmic Vein 
The Intercavernous Sinuses 
The Superior Petrosal Sinus 
The Inferior Petrosal Sinus 
The Basilar Plexus 
The Emissary Veins . 



646 
646 
647 
647 
647 
648 
648 
649 
650 
651 
652 
652 
652 
652 
652 
652 
653 
653 
653 

654 
654 
655 
655 
657 
658 
658 
658 
658 
659 
659 
659 
659 
659 
660 
660 



The Veins of the Upper Extremity and 
Thorax. 

The Superficial Veins of the Upper Extremity 660 

Digital Veins 660 

The Cephalic Vein 661 

The Accessory Cephalic Vein . . 662 

The Basilic Vein 662 

The Median Antibrachial Vein . . . 662 

The Deep Veins of the Upper Extremity . 663 

Deep Veins of the Hand 663 

Deep Veins of the Forearm .... 663 

The Brachial Veins 663 

The Axillary Vein 663 

The Subclavian Vein 664 

Tributaries 664 

The Veins of the Thorax 664 

The Innominate Veins 664 

The Right Innominate Vein . . 664 

The Left Innominate Vein . . . 666 

Tributaries 666 

Peculiarities . . ... 666 

The Internal Mammary Veins . . . 666 

The Inferior Thyroid Veins .... 666 

The Highest Intercostal Vein . . . 666 

The Superior Vena Cava .... 666 

Relations 667 

The Azygos Vein 667 

Tributaries 667 

The Hemiazygos Veins . . 667 



The Veins of the Thora.x — 
The Azygos Vein — 

The Accessory Hemiazygos 

Veins 667 

The Bronchial Veins 667 

The Veins of the Vertebral Column . . . 667 

The External Vertebral Venous Plexuses 668 

The Internal Vertebral Venous Plexuses 668 

The Basivertebral Veins 668 

The Intervertebral Veins .... 669 

The Veins of the Medulla Spinalis . . 669 

The Veins of the Lower Extremity, Abdomen, 
and Pelvis. 

The Superficial Veins of the Lower Extremity 669 

The Dorsal Digital Veins 669 

The Great Saphenous Vein .... 669 

Tributaries . 670 

The Small Saphenous Vein .... 670 

The Deep Veins of the Lower Extremity . 671 
The Plantar Digital Veins . . . .671 

The Posterior Tibial Veins .... 672 

The Anterior Tibial Veins .... 672 

The Popliteal Vein 672 

The Femoral Vein 672 

The Deep Femoral Vein . . . 672 

The Veins of the Abdomen and Pelvis . . 672 

The External Iliac Vein 672 

Tributaries 672 

The Hypogastric Veins 673 

Tributaries 673 

The Hemorrhoidal Plexus .... 676 

The Pudendal Plexus 676 

The Vesical Plexus 676 

The Dorsal Veins of the Penis . . . 676 

The Uterine Plexuses 676 

The Vaginal Plexuses 677 

The Common Iliac Veins .... 677 

The Middle Sacral Veins ... 677 

Peculiarities 677 

The Inferior Vena Cava 677 

Relations 678 

Peculiarities 678 

Applied Anatomy 678 

Tributaries 678 

Lumbar Veins 678 

Spermatic Veins .... 678 

Ovarian Veins 679 

Renal Veins 679 

Suprarenal Veins .... 679 

Inferior Phrenic Veins . . . 679 

Hepatic Veins 680 

The Portal System of Veins. 

The Portal Vein 681 

Tributaries 681 

The Lienal Vein 681 

Tributaries 681 

The Superior Mesenteric Vein . . 682 

Tributaries 682 

The Coronary Vein 682 

The Pyloric Vein 682 

The Cystic Vein 682 

The Parumbilical Veins .... 682 



THE LYMPHATIC SYSTEM. 



The Development of the Lymphatic Vessels 683 

Lymphatic Capillaries 684 

Distribution 684 

Lymphatic Vessels 687 

Structure of Lymphatic Vessels .... 687 

The Lymph Glands 688 

Structure of Lymph Glands .... 688 

Hemolymph Nodes 690 

Lymph .690 

The Thoracic Duct. 

The Cisterna Chyli 691 

Tributaries 691 

The Right Lymphatic Duct 691 

Tributaries 692 



The Lymphatics 



OF the 
Neck. 



Head, Face, and 



The Lymph Glands of the Head . 
The Occipital Glands . 
The Posterior Auricular Glands 
The Anterior Auricular Glands 
The Parotid Glands . . . 
The Facial Glands 
The Deep Facial Glands . 
The Lingual Glands 
The Retropharyngeal Glands 
The Lymphatic Vessels of the Scalp 
The Lymphatic Vessels of the Auricula 

and External Acoustic Meatus 
The Lymphatic Vessels of the Face 



692 
692 
693 
693 
693 
694 
694 
694 
694 
694 

694 
695 



20 



CONTENTS 



The Lymph Glands of the Head — 

The Lymphatic Vessels of the Nasal 

Cavities 695 

The Lymphatic Vessels of the Mouth . 695 
The Lymphatic Vessels of the Palatine 

Tonsil 695 

The Lymphatic Vessels of the Tongue . 696 

The Lymph Glands of the Neck .... 697 

The Submaxillary Glands .... 697 

The Submental or Suprahyoid Glands . 697 

The Superficial Cervical Glands . . . 697 

The Anterior Cervical Glands . . . 697 
The Deep Cervical Glands . . . .697 
The Lymphatic Vessels of the Skin and 

Muscles of the Neck 698 



The Lymphatics of the Upper Extremity. 

The Lymph Glands of the Upper Extremity 699 

The Superficial Lymph Glands . . . 699 

The Deep Lymph Glands .... 699 

The Axillary Glands .... 699 

The Lymphatic Vessels of the L^pper 

Extremity 700 

The Superficial Lymphatic Vessels . . 700 
The Deep Lymphatic Vessels . . .701 



The Lymphatics of the Lower Extremity. 

The Lymph Glands of the Lower Extremity 701 

The Anterior Tibial Gland .... 701 

The Popliteal Glands 701 

The Inguinal Glands 702 

The Lymphatic Vessels of the Lower 

Extremity 703 

The Superficial Lymphatic Vessels . . 703 

The Deep Lymphatic Vessels . . . 703 



The Lymphatics of the Abdomen and Pelvis. 

The Lymph Glands of the Abdomen and 

Pelvis 703 

The Parietal Glands 703 

The External Iliac Glands ... 703 

The Common Iliac Glands . . . 704 

The Epigastric Glands .... 704 

The Iliac Circumflex Glands . . 704 

The Hypogastric Glands . 704 

The Sacral Glands 704 

The Lumbar Glands .... 705 
The Lymphatic Vessels of the Abdomen and 

Pelvis 706 

The Superficial Vessels 706 

The Deep Vessels 706 

The Lymphatic Vessels of the 

Perineum and External Genitals 706 

The Visceral Glands 706 

The Gastric Glands 706 

The Hepatic Glands .... 706 

The Pancreaticolienial Glands . . 706 

The Superior Mesenteric Glands . . 709 

The Mesenteric Glands .... 709 

The Ileocolic Glands .... 709 

The Mesocolic Glands .... 709 

The Inferior Mesenteric Glands 710 

The Lymphatic Vessels of the Abdominal 

and Pelvic Viscera 710 



The Lymphatic Vessels of the Abdomina 
and Pelvic Viscera — 
The Lymphatic Vessels of the Subdia- 
phragmatic Portions of the Digestive 

Tube . 710 

The Lymphatic Vessels of the Stomach 710 
The Lymphatic Vessels of the Duodenum 710 
The Lymphatic Vessels of the Jejunum 

and Ileum 710 

The Lymphatic Vessels of the Vermiform 

Process and Cecum 710 

The Lymphatic Vessels of the Colon . 711 
The Lymphatic Vessels of the Anus, 

Anal Canal, and Rectum . . . .711 
The Lymphatic Vessels of the Liver . 711 
The Lymphatic Vessels of the Gall- 
bladder 711 

The Lymphatic Vessels of the Pancreas 711 
The Lymphatic Vessels of the Spleen and 

Suprarenal Glands 711 

The Lymphatic Vessels of the Urinary 

Organs 712 

The Lymphatic Vessels of the 

Kidney 712 

The Lymphatic Vessels of the Ureter 71 2 
The Lymphatic Vessels of the 

Bladder 712 

The Lymphatic Vessels of the 

Prostate 713 

The Lymphatic Vessels of the 

Urethra 713 

The Lymphatic Vessels of the Repro- 
ductive Organs 713 

The Lymphatic Vessels of the 

Testes . . 713 

The Lymphatic Vessels of the 

Ductus Deferens 713 

The Lymphatic Vessels of the Ovary 714 
The Lymphatic Vessels of the 

Uterine Tube 714 

The Lymphatic Vessels of the 

Uterus 714 

The Lymphatic Vessels of the 
Vagina 714 



The Lymphatics of the Thorax. 

The Parietal Lymph Glands 715 

The Sternal Glands 715 

The Intercostal Glands 715 

The Diaphragmatic Glands .... 715 

The Superficial Lymphatic Vessels of the 

Thoracic Wall 715 

The Lymphatic Vessels of the Mamma. 715 

The Deep Lymphatic Vessels of the Thoracic 

Wall 716 

The Visceral Lymph Glands . . . 717 

The Anterior Mediastinal Glands . . 717 

The Posterior Mediastinal Glands . . 717 

The Tracheobronchial Glands . . . 717 

The Lymphatic Vessels of the Thoracic 

Viscera 718 

The Lymphatic Vessels of the Heart . 718 
The Lymphatic Vessels of the Lungs 718 
The Lymphatic Vessels of the Pleura . 719 
The Lymphatic Vessels of the Thymus 719 
The Lymphatic Vessels of the Eso- 
phagus 719 



NEUROLOGY. 



Structure of the Nervous System. 

Neuroglia 722 

Nerve Cells 722 

Nerve Fibers 724 

Wallerian Degeneration 727 

Non-medullated Fibers 728 

Structure of the Peripheral Nerves and 

Ganglia • 728 

Origins and Terminations of Nerves . . . / 29 



Ganglia 730 

Neuron Theory 732 

Fasciculi, Tracts or Fiber Systems . . 732 



Development of the Nervous System. 

The Medulla Spinalis 733 

The Spinal Nerves 735 

The Brain 736 



CONTENTS 



21 



The Brain— 

The Hind-brain or Rhombencephalon . 738 

The Mid-brain or Mesencephalon . . 741 

The Fore-brain or Prosencephalon 741 

The Diencephalon 742 

The Telencephalon 743 

The Commissures 746 

Fissures and Sulci 747 

The Cranial Nerves 748 



The Spinal Cord or Medulla Spinalis. 

Enlargements 751 

Fissures and Sulci 752 

The Anterior Median Fissure 752 

The Posterior Median Sulcus . . 752 

The Internal Structure of the Medulla 

Spinalis 753 

The Gray Substance 753 

Structure of the Gray Substance . 755 

The White Substance 758 

Nerve Fasciculi 759 

Roots of the Spinal Nerves 764 

The Anterior Nerve Root .... 764 

The Posterior Root 764 



The Brain or Encephalon. 
General Considerations and Divisions 



766 



The Hind-brain or Rhombencephalon. 

The Medulla Oblongata 767 

The Anterior Median Fissure . . 767 

The Posterior Median Fissure . . . 767 
Internal Structure of the Medulla 

Oblongata 775 

The Cerebrospinal Fasciculi . 775 
Gray Substance of the Medulla 

Oblongata 779 

Inferior Peduncle 782 

Formatio Reticularis .... 784 

The Pons 785 

Structure 785 

The Cerebellum 788 

Lobes of the Cerebellum 788 

Internal Structure of the Cerebellum . 791 

The White Substance . . . .791 

Projection Fibres . .791 

The Gray Substance .... 794 

Microscopic Appearance of the 

Cortex 794 

The Fourth Ventricle 797 

Angles 797 

Lateral Boundaries 797 

Choroid Plexuses 798 

Openings in the Roof 798 

Rhomboid Fossa 798 

The Mid-brain or Mesencephalon. 

The Cerebral Peduncles 800 

Structure of the Cerebral Peduncles . 801 

The Gray Substance .... 802 

The White Substance .... 803 

The Corpora Quadrigemina 805 

Structure of the Corpora Quadrigemina 806 

The Cerebral Aqueduct 806 

The Fore-brain or Prosencephalon. 

The Diencephalon 807 

The Thalamencephalon 808 

Structure 810 

Connections 810 

The Metathalamus 811 

The Epithalamus 812 

The Hypothalamus 812 

The Optic Chiasma 814 

The Optic Tracts 814 

The Third Ventricle ....".. 815 

The Interpeduncular Fossa .... 816 

The Telencephalon 817 



The Cerebral Hemispheres 817 

The Longitudinal Cerebral Fissure . 818 
The Surfaces of the Cerebral Hemi- 
spheres 818 

The Lateral Cerebral Fissure . . .819 

The Central Sulcus 819 

The Parietooccipital Fissure .... 820 

The Calcarine Fissure 820 

The Cingulate Sulcus 820 

The Collateral Fissure 820 

The Sulcus Circularis 821 

The Lobes of the Hemispheres . . . 821 

The Frontal Lobe 821 

The Parietal Lobe 822 

The Occipital Lobe 823 

The Temporal Lobe 823 

The Insula 825 

The Limbic Lobe 825 

The Rhinencephalon 826 

The Olfactory Lobe 826 

The Interior of the Cerebral Hemi- 
spheres 827 

The Corpus Callosum .... 828 

The Lateral Ventricles .... 829 

The Fornix 838 

The Interventricular Foramen . . 840 

The Anterior Commissure . . . 840 

The Septum Pellucidum .... 840 
The choroid Plexus of the Lateral 

Ventricle 840 

Structure of the Cerebral Hemi- 
spheres 842 

Structure of the Cerebral Cortex . . 845 

Special Types of Cerebral Cortex . . 847 

Weight of Encephalon 848 

Cerebral Localization 849 

Composition and Central Connections of the Spinal 

Nerves. 

The Intrinsic Spinal Reflex Paths . . . 850 
Sensory Pathways from the Spinal Cord 

to the Brain 851 

Composition and Central Connections of the Cranial 
Nerves. 

The Hypoglossal Nerve 855 

The Accessory Nerve 855 

The Vagus Nerve 855 

The Glossopharyngeal Nerve 856 

The Acoustic Nerve 857 

The Vestibular Nerve 860 

The Facial Nerve 861 

The Abducens Nerve 861 

The Trigeminal Nerve 862 

The Trochlear Nerve 863 

The Oculomotor Nerve 863 

The Optic Nerve 864 

The Olfactory Nerves 866 

Pathways from the Brain to the Spinal Cord. 

The Motor Tract 870 

The Meninges of the Brain and Medulla Spinalis. 

The Dura Mater 872 

The Cranial Dura Mater .... 872 

Processes 873 

Structure 875 

The Spinal Dura Mater 875 

Structure 876 

The Arachnoid 876 

The Cranial Part 876 

The Spinal Part 876 

Structure 876 

The Subarachnoid Cavity .... 876 

The Subarachnoid Cisternse .... 876 

The Arachnoid Villi 878 

Structure 878 

The Pia Mater 878 

The Cranial Pia Mater 879 

The Spinal Pia Mater 879 

The Ligamentum Denticulatum . . 880 



22 



CONTENTS 



The Cerebrospinal Fluid 

The Cranial Nerves. 
The Olfactory Nerves 
The Optic Nerve. 



The Optic Chiasma 
The Optic Tract 



The Oculomotor Nerve 
The Trochlear Nerve . 
The Trigeminal Nerve. 



The Semilunar Ganglion . 
The Ophthalmic Nerve 

The Lacrimal Nerve . 

The Frontal Nerve 

The Nasociliary Nerve 

The Ciliary Ganglion . 
The Maxillary Nerve . 

Branches .... 

The Middle Meningeal Nerve 
The Zygomatic Nerve 
The Sphenopalatine . 
The Posterior Superior Alveolar 
The Middle Superior Alveolar 
The Anterior Superior Alveolar 
The Inferior Palpebral 
The External Nasal ... 
The Superior Labial 
The Sphenopalatine Ganglion 
The Mandibular Nerve .... 

Branches 

The Nervus Spinosus 
The Internal Pterygoid Nerve 
The Masseteric Nerve 
The Deep Temporal Nerves 
The Buccinator Nerve . 
The External Pterygoid Nerve 
The Auriculotemporal Nerve 
The Lingual Nerve . 
The Inferior Alveolar Nerve 
The Otic Ganglion 
The Submaxillary Ganglion 
Trigeminal Nerve Reflexes ... 



The Abducent Nerve 



880 



881 



883 
884 

884 

885 



886 
887 
887 
887 
888 
888 
889 
889 
889 
889 
890 
890 
891 
891 
891 
891 
891 
891 
893 
894 
894 
894 
894 
895 
895 
895 
895 
895 
896 
897 
898 
899 

899 



The Ganglion Nodosum — 
The Meningeal Branch 
The Auricular Branch 
The Pharyngeal Branch . 
The Superior Laryngeal Nerve 
The Recurrent Nerve 
The Superior Cardiac Branches 
The Inferior Cardiac Branches 
The Anterior Bronchial Branches 
The Posterior Bronchial Branches 
The Esophageal Branches 
The Gastric Branches 
The Celiac Branches 
The Hepatic Branches 



911 
911 
911 
912 
912 
912 
912 
913 
913 
913 
913 
913 
913 



The Accessory Nerve. 



The Facial Nerve. 

The Greater Superficial Petrosal Nerve . 903 

The Nerve to the Stapedius 904 

The Chorda Tympani Nerve 904 

The Posterior Auricular Nerve .... 905 

The Digastric Branch 905 

The Stylohyoid Branch 905 

The Temporal Branches 905 

The Zygomatic Branches 905 

The Buccal Branches 905 

The Mandibular Branch 905 

The Cervical Branch 905 

The Acoustic Nerve. 

The Cochlear Nerve 906 

The Vestibular Nerve 906 

The Glossopharyngeal Nerve. 

The Superior Ganglion 908 

The Petrous Ganglion 908 

The Tympanic Nerve 909 

The Carotid Branches 909 

The Pharyngeal Branches .... 909 

The Muscular Branches 909 

The Tonsillar Branches 909 

The Lingual Branches 909 

The Vagus Nerve. 

The Jugular Ganglion 911 

The Ganglion Nodosum 911 



The Cranial Part 913 

The Spinal Part 913 

The Hypoglossal Nerve. 

Branches of Communication 915 

Branches of Distribution 916 

The Meningeal Branches .... 916 

The Descending Ramus 916 

The Thyrohyoid Branch 916 

The Muscular Branches 916 



The Spinal Nerves. 



Nerve Roots 




. 916 


The Anterior Root 




. 916 


The Posterior Root . . . 




. 916 


The Spinal Ganglia 




. 917 


Structure 




. 917 


Connections -with SjTnpathetic 




. 920 


Structure 




. 920 


Divisions of the Spinal Nerves 




. 921 


The Posterior Divisions . 




. 921 


The Cervical Nerves 




. 921 


The Thoracic Nerves 




. 923 


The Lumbar Nerves 




. 924 


The Sacral Nerves 




. 924 


The Coccygeal Nerve 




. 925 


The Anterior Divisions 




. 925 


The Cervical Nerves 




. 925 


The Cervical Plexus 




. 925 


Great Auricular Nerve 


. 926 


Cutaneous Cervical N 


Brve 927 


Supraclavicular Nerve 


s . 928 


Communicantes Cervicales 928 


Phrenic Nerve . 


. 928 


The Brachial Plexus . 


. 930 


Relations . 


. 931 


Dorsal Scapular Nerv 


e . 932 


Suprascapular Nerve 


. 932 


Nerve to Subclavius 


. 933 


Long Thoracic Nerve 


. 933 


Anterior Thoracic Nerves 933 


Subscapular Nerves 


. 933 


Thoracodorsal Nerve 


. 934 


Axillarv Nerve 


. 934 


Musculocutaneous Nerve 935 


Medial Antibrachial C 


uta- 


neous Nerve 


. 937 


Medial Brachial Cut£ 


i- 


neous Nerve 


. 937 


Median Nerve . 




. 938 


L'lnar Nerve 




. 939 


Radial Nerve . 




. 943 


The Thoracic Nerves 




. 944 


First Thoracic Nerve 




. 945 


Upper Thoracic Nerves 


. 945 


Lower Thoracic Nerves 


. 948 


The Lumbosacral Plexus 


. 948 


The Lumbar Nerves 


. 948 


The Lumbar Plexus 


. 949 


Iliohypogastric N( 


jrve 950 


Ilioinguinal Nerve 


. 952 


Genitofemoral Ne 


rve 953 


Lateral Femoral C 


uta- 


neous Nerve 


. 953 


Obturator Ner 


ve 


. 953 



CONTENTS 



23 



Dmsions of the Spinal Nerves — 
The Anterior Divisions — 

The Lumbosacral Plexus — 
The Lumbar Nerves — 

The Lumbar Plexus — 

Accessory Obturator 
Nerve .... 
Femoral Nerve 
Saphenous Nerve. 
The Sacral and Coccygeal 

Nerves 

The Sacral Plexus 
Relations 

Nerve to Quadratus 
Femoris and 
Gemellus Inferior 
Nerve to Obturator 
Internus and Ge- 
mellus Superior . 
Nerve to Piriformis 



Superior 
Nerve . 

Inferior 
Nerve . 

Posterior 



Gluteal 
Gluteal 



Femoral 
Cutaneous Nerve 
Sciatic Nerve 
Tibial Nerve 
Lateral Plantar Nerve 
Common Peroneal 
Nerve .... 
Deep Peroneal Nerve 
Superficial Peroneal 
Nerve .... 
The Pudendal Plexus 

Perforating Cuta- 
neous Nerve 
Pudendal Nerve 
Anococcygeal Nerve 



955 
955 
956 

957 
957 
957 



957 



958 
959 

959 

959 

959 
960 
960 
963 

964 
965 

966 
966 

967 
967 
968 



The Cephalic Portion of the Sympathetic 
System. 

The Internal Carotid Plexus .... 977 
The Cavernous Plexus 978 



The Cervical Portion of the Sympathetic 
Systern. 



The Superior Cervical Ganglion 
Branches 

The Middle Cervical Ganglion 
Branches 

The Inferior Cervical Ganglion 
Branches 



978 
978 
979 
979 
980 
981 



The Sympathetic Nerves. 

The Cranial Sympathetics 970 

The Sacral Sympathetics 973 

The Thoracolumbar Svmpathetics . . . 974 

The Sympathetic Trunks 976 

Connections with the Spinal Nerves . . 976 

Development 977 



The Thoracic Portion of the Sympathetic 
System. 

The Greater Splanchnic Nerve .... 981 
The Lesser Splanchnic Nerve .... 981 
The Lowest Splanchnic Nerve .... 981 

The Abdominal Portion of the Sympathetic 

System .... 982 



The Pelvic Portion of the Sympathetic 
System .... 



984 



The Great Plexuses of the Sympathetic System. 

The Cardiac Plexus 984 

The Celiac Plexus 985 

Phrenic Plexus 985 

Hepatic Plexus 986 

Lienal Plexus 986 

Superior Gastric Plexus 987 

Suprarenal Plexus 987 

Renal Plexus ......... 987 

Spermatic Plexus 987 

Superior Mesenteric Plexus . . . 987 

Abdominal Aortic Plexus .... 987 

Inferior Mesenteric Plexus .... 987 

The Hypogastric Plexus 987 

The Pelvic Plexuses 987 

The Middle Hemorrhoidal Plexus . . 988 

The Vesical Plexus 988 

The Prostatic Plexus 988 

The Vaginal Plexus 989 

The Uterine Plexus 989 



THE ORGANS OF THE SENSES AND THE COMMON INTEGUMENT. 



The Peripheral Organs of the Special 

Senses. 

The Organs of Taste. 

Structure 991 

The Organ of Smell. 

The External Nose 992 

Structure 992 

The Nasal Cavity 994 

The Lateral Wall 994 

The Medial Wall 995 

The Mucous Membrane .... 996 
Structure 996 

The Accessory Sinuses of the Nose . . . 998 

The Frontal Sinuses 998 

The Ethmoidal Air Cells .... 998 

The Sphenoidal Sinuses 998 

The Maxillary Sinus 999 

The Organ of Sight. 

Development 1001 

The Tunics of the Eye 1005 

The Fibrous Tunic 1005 

The Sclera 1005 

Structure 1006 

The Cornea 1006 

Structure 1007 



The Tunics of the Eye — 

The Vascular Tunic 1009 

The Choroid 1009 

Structure 1010 

The Ciliary Body 1010 

Structure 1011 

The Iris 1012 

Structure 1013 

Membrana Pupillaris .... 1014 

The Retina 1014 

Structure 1015 

The Refracting Media 1018 

The Aqueous Humor 1018 

The Vitreous Body 1018 

The Crystalline Lens 1019 

Structure 1020 

The Accessory Organs of the Eye . . . 1021 

The Ocular Muscles . . . . . . 1021 

Levator Palpebrae Superior! s . . 1021 

The Recti 1022 

Obliquus Oculi Superior . . . 1022 

Obliquus Oculi Inferior . . . 1023 

The Fascia Bulb 1024 

The Orbital Fascia 1025 

The Eyebrows 1025 

The Eyelids 1025 

The Lateral Palpebral Commis- 

^ sure 1025 

The Eyelashes 1025 

Structure of the Eyelids . . 1025 

The Tarsal Glands 1026 



24 



CONTENTS 



The Accessory Organs of the Eye — 

Structure of the Tarsal Glands 
The Conjunctiva 

The Palpebral Portion 
The Bulbar Portion 
The Lacrimal Apparatus 
The Lacrimal Gland 

Structure 
The Lacrimal Ducts 
The Lacrimal Sac . 

Structure 
The Nasolacrimal Duct 

The Organ of Hearing. 



1026 
1026 
1027 
1027 
1028 
1028 
1028 
1028 
1028 
1029 
1029 



Development 1029 

The External Ear 1033 

The Auricula or Pinna 1033 

Structure 1034 

The External Acoustic Meatus . 1036 

Relations 1037 

The Middle Ear or Tympanic Cavity . 1037 

The Tegumental ^yall or Roof . . . 1038 

The Jugular Wall or Floor .... 1038 

The Membranous or Lateral Wall 1038 

The Tympanic Membrane .... 1039 

Structure 1039 

The Labvrinthic or Medial Wall . . 1040 

The Mastoid or Posterior Wall . . 1042 

The Carotid or Anterior Wall . 1042 

The Auditorj- Tube 1042 

The Auditory Ossicles 1044 

The Malleus 1044 

The Incus 1044 

The Stapes 1045 

Articulations of the Auditory Ossicles 1045 

Ligaments of the Ossicles .... 1045 

The Muscles of the Tympanic Cavity 1046 

The Tensor Tympani .... 1046 

The Stapedius 1046 

The Internal Ear or Labyrinth .... 1047 

The Osseous Labyrinth 1047 



The Internal Ear or Labyrinth — 
The Osseous Labyrinth — 

The Vestibule 

The Bony Semicircular Canals 

The Cochlea 
The Membranous Labyrinth 

The Utricle .... 

The Saccule .... 

The Semicircular Ducts 
Structure 

The Ductus Cochlearis 

The BasUar Membrane 

The Spiral Organ of Corti 

Hair Cells .... 



1047 
1049 
1050 
1051 
1051 
1052 
1052 
1052 
1054 
1056 
1056 
1057 



Peripheral Terminations of Xerves of General 
Sensations. 

Free Nerve-endings 1059 

Special End-organs 1059 

End-bulbs of Krause 1060 

Tactile Corpuscles of Grandry .... 1060 

Pacinian Corpuscles 1060 

Corpuscles of Golgi and Mazzoni . . 1061 

Tactile Corpuscles of Wagner and Meissner 1061 

Corpuscles of Ruffini 1061 

Neurotendinous Spindles 1061 

Neuromuscular Spindles 1061 



The Comon Integument. 

The Epidermis, Cuticle, or Scarf Skin . . 1062 
The Corium, Cutis Vera, Dermis, or True 

Skin 1065 

Development 1066 

The Appendages of the Skin. 

The NaUs 1066 

The Hairs 1067 

The Sebaceous Glands 1069 

The Sudoriferous or Sweat Glands . . . 1070 



SPLANCHNOLOGY. 



The Respiratory Apparatus. 



Development 








107] 


The Larynx. 


The Cartilages of the Larynx .... 1073 


The Thyroid Cartilage . 








1073 


The Cricoid Cartilage 








1074 


The Arytenoid Cartilage 








1075 


The Corniculate Cartilages 








1075 


The Cuneiform Cartilages 








1075 


The Epiglottis . . . 








1075 


Structure 








1076 


The Ligaments of the Larynx 








1076 


The Extrinsic Ligaments 








1076 


The Intrinsic Ligaments 








1077 


The Interior of the Larynx . 








1078 


The Ventricular Folds . 








1079 


The Vocal Folds . . . 








1079 


The Ventricle of the Larynx 








1080 


The Rima Glottidis . . 








1080 


The Muscles of the Larynx . 








1081 


Cricothyreoideus 








1081 


Cricoarytsenoideus Posterior 






1082 


Cricoarytsenoideus Lateralis 






1082 


Arytaenoideus .... 






1082 


Thyreoarytaenoideus 








1083 



The Trachea and Bronchi. 

Relations 1084 

The Right Bronchus 1085 

The Left Bronchus 1085 

Structure 1086 



The Pleurce. 

Reflections of the Pleura 1088 

Pulmonary Ligament 1090 

Structure of Pleura 1090 

The Mediastinum. 

Superior Mediastinum 1090 

Anterior Mediastinum 1092 

Middle Mediastinum 1092 

Posterior ^Mediastinum 1093 

The Lungs. 

The Apex of the Lungs 1094 

The Base of the Lungs 1094 

Surfaces of the Lungs 1094 

Borders of the Lungs 1096 

Fissures and Lobes of the Lungs . . . 1096 

The Root of the Lung 1097 

Di\-isions of the Bronchi 1097 

Structure of the Lungs 1098 

The Digestive Apparatus. 

The Digestive Tube 1100 

The Development of the Digestive 

Tube 1101 

The Mouth 1101 

The Salivary Glands .... 1102 

The Tongue 1102 

The Palatine TonsOs .... 1103 
The Further Development of the 

Digestive Tube 1103 

The Rectum and Anal Canal . 1108 



CONTENTS 



25 



The Mouth. 



The Abdomen. 



The Vestibule of the Mouth 1110 

The Mouth Cavity Proper 1110 

Structure 1110 

The Lips 1111 

The Labial Glands 1111 

The Cheeks 1112 

Structure 1112 

The Gums 1112 

The Palate 1112 

The Hard Palate 1112 

The Soft Palate 1112 

The Teeth 1112 

General Characteristics 1114 

The Permanent Teeth 1115 

The Canine Teeth 1117 

The Premolar or Bicuspid Teeth . 1118 

The Molar Teeth 1118 

The Deciduous Teeth 1118 

Structure of the Teeth 1118 

Development of the Teeth .... 1121 
Development of the Deciduous 

Teeth 1122 

Development of the Permanent 

Teeth 1124 

Eruption of the Teeth 1124 

The Tongue 1125 

The Root of the Tongue .... 1125 

The Apex of the Tongue . . . . 1125 

The Dorsum of the Tongue . . . 1125 

The Papilla of the Tongue . . . . 1126 

The Muscles of the Tongue . . . 1128 

Genioglossus 1129 

Hyoglossus 1129 

Chondroglossus 1130 

Styloglossus 1130 

Longitudinalis Linguae Superior 1130 

Longitudinalis Linguae Inferior 1130 

Transversus Linguae .... 1130 

Verticalis Linguae 1131 

Structure of the Tongue . . . 1131 

Glands of the Tongue 1131 

The Salivary Glands 1132 

The Parotid Gland 1132 

Structures within the Gland . . 1134 

The Parotid Duct 1134 

Structure 1134 

The Submaxillary Gland . . . . 1135 

The Submaxillary Duct . . . 1135 

The Sublingual Gland 1136 

Structure of the Salivary Gland . . 1136 

Accessory Glands 1137 

The Fauces. 



The Glossopalatine Arch .... 


1137 


The Pharyngopalatine Arch .... 


1137 


The Palatine Tonsils 


1137 


Structure 


1139 


The Palatine Aponeurosis .... 


1139 


The Muscles of the Palate . 


1139 


Levator Veli Palatini . 


1139 


Tensor Veli Palatini . . . 


1139 


Musculus U\'ulse .... 


1139 


Glossopalatinus .... 


1139 


Paryngopalatinus .... 


1139 


The Pharynx. 




The Nasal Part of the Pharynx . 


1141 


The Oral Part of the Pharynx 


1142 


The Laryngeal Part of the Pharynx 


1142 


The Muscles of the Pharj'nx 


1142 


Constrictor Pharyngis Inferior . 


1142 


Constrictor Pharyngis Medius . 


1142 


Constrictor Pharyngis Superior 


1142 


Stylopharyngeus 


. 1142 


Salpingopharyngeus 


. 1142 


Structure of the Pharynx .... 


. 1143 


The Esophagus. 




Relations 


. 1145 


Structure 


. 1146 



Boundaries of the Abdomen 1147 

The Apertures in the Walls of the Abdomen 1147 

Regions of the Abdomen 1147 

The Peritoneum .1149 

Vertical Dispositions of the Main Peri- 
toneal Cavity 1150 

Vertical Disposition of the Omental 

Bursa 1152 

Horizontal Disposition of the Peri- 
toneum 1153 

In the Pelvis 1153 

In the Lower Abdomen . . . 1154 

In the Upper Abdomen . . . 1155 

The Omenta 1156 

The Mesenteries 1157 

The Peritoneal Recesses or Fossae . . 1158 

The Duodenal Fossae .... 1159 

The Cecal Fossffi 1160 

The Intersigmoid Fossa . . . 1161 

The Stomach. 

Openings of the Stomach 1161 

Curvatures of the Stomach 1162 

Surfaces of the Stomach 1162 

Component Parts of the Stomach . . . 1163 

Position of the Stomach 1163 

Interior of the Stomach 1164 

Pyloric Valve 1164 

Structure of the Stomach 1164 

The Gastric Glands 1166 

The Small Intestine. 

The Duodenum 1169 

Relations 1169 

The Jejunum and Ileum 1170 

Meckel's Diverticulum 1172 

Structure 1172 

The Large Intestine. 

The Cecum 1177 

The Vermiform Process or Appendix . 1178 

Structure 1179 

The Colic Valve 1179 

The Colon 1180 

The Ascending Colon 1180 

The Transverse Colon 1180 

The Descending Colon 1181 

The Iliac Colon 1182 

The Sigmoid Colon 1182 

The Rectum 1183 

Relations of the Rectum . . . . 1184 

The Anal Canal 1184 

Structure of the Colon 1184 

The Liver. 

Surfaces of the Liver 1188 

Fossae of the Liver 1191 

Lobes of the Liver 1191 

Ligaments of the Liver 1192 

Fixation of the Liver 1193 

Development of the Liver 1193 

Structure of the Liver 1195 

Excretory Apparatus of the Liver . . . 1197 

The Hepatic Duct 1197 

The Gall-bladder 1197 

Relations 1197 

Structure 1198 

The Common BUe Duct .... 1198 

Structure 1199 

The Pancreas. 

Relations 1200 

The Pancreatic Duct 1202 

Development of the Pancreas .... 1202 

Structure 1203 



26 



CONTENTS 



The Urogenital Apparatus. 

Development of the Urinary and Generative Organs 

The Pronephros and Wolffian Duet . . 1205 
The Mesonephros, Miillerian Duct, and 

Genital Gland 1205 

The Miillerian Ducts 1206 

Genital Glands 1207 

The Ovary 1207 

The Testis 1210 

Descent of the Ovaries 1211 

The Metanephros and the Permanent 

Kidney 1211 

The Urinary Bladder 1212 

The Prostate 1213 

External Organs of Generation . . . . 1213 

The Urethra , 1215 

The Urinary Organs. 

The Kidneys 1215 

Relations 1215 

Surfaces 1215 

Borders 1218 

Extremities 1219 

Fixation of the Kidney .... 1220 

General Structure of the Kidney . . 1220 

The Ureters 1225 

The Ureter Proper 1226 

Structure 1227 

Variations 1227 

The Urinary Bladder 1227 

The Empty Bladder 1227 

The Distended Bladder 1228 

The Bladder in the Child .... 1229 

The Eemale Bladder . . . . . 1230 

The Ligaments of the Bladder . . . 1231 

The Interior of the Bladder . . . 1231 

Structure 1232 

Abnormalities 1233 

The Male Urethra 1234 

The Prostatic Portion 1234 

The Membranous Portion .... 1235 

The Cavernous Portion 1235 

Structure 1235 

Congenital Defects 1235 

The Female Urethra 1236 

Structure 1236 

Th Male Genital Organs. 

The Testes and their Coverings .... 1236 

The Scrotum 1237 

The Intercrural Fascia 1238 

The Cremaster Muscle 1238 

The Infundibuliform Fascia . . . 1239 

The Tunica Vaginalis 1239 

The Inguinal Canal 1239 

The Spermatic Cord 1239 

Structure of the Spermatic Cord . 1239 

The Testes 1240 

The Epididymis 1242 

Appendages of the Testis and Epi- 
didymis 1242 

The Tunica Vaginalis . . 1242 

The Tunica Albuginea . . 1242 

The Tunica Vasculosa . . 1243 

Structure 1243 

Peculiarities 1245 

The Ductus Deferens 1245 

The Ductuli Aberrantes .... 1246 

Paradidymis 1246 

Structure 1246 

The Vesiculae Seminales 1246 

Structure 1247 

The Ejaculatory Ducts 1247 

Structure 1247 

The Penis 1247 

The Corpora Cavernosa Penis . . . 1248 

The Corpus Cavernosum Urethrse . 1248 

Structure of the Penis 1250 



The Prostate 1251 

Structure 1253 

The Bulbourethral Glands 1253 

Structure 1253 

The Female Genital Organs. 

The Ovaries 1254 

The Epoophoron 1255 

The Paroophoron . - 1255 

Structure 1255 

Vesicular Ovarian Follicles .... 1256 

Discharge of the 0\'um 1256 

Corpus Luteum 1256 

The Uterine Tube 1257 

Structure 1257 

The Uterus 1258 

The Body 1259 

The Cervix 1259 

The Interior of the Uterus .... 1260 

The Ca\ity of the Body . . . 1260 

The Canal of the Cervix . . . 1260 

The Ligaments of the Uterus . . . 1260 

Structure 1262 

The Vagina 1264 

Relations 1264 

Structure 1264 

The External Organs 1264 

The Mons Pubis 1265 

The Labia Majora 1265 

The Labia Minora 1265 

The Clitoris 1266 

The Vestibule 1266 

The Bulb of the Vestibule .... 1266 

The Greater Vestibular Glands . . 1266 

The Mammae 1267 

The Mammary Papilla or Nipple . . 1267 

Development 1267 

Structure 1267 



The Ductless Glands. 

The Thyroid Gland. 

Development 1270 

Structure 1271 

The Parathyroid Glands. 

Development 1272 

Structure .... 1273 

The Thymus. 

Development 1273 

Structure 1274 

The Hypophysis Cerebri. 

Development 1276 

The Pineal Body. 

Structure 1277 

The Chromaphil and Cortical Systems. 

Development 1277 

The Suprarenal Glands 1278 

Development 1278 

Relations 1278 

Accessory Suprarenals 1279 

Structure 1279 

Glomus Caroticum 1281 

Glomus Coccygeum 1281 

The Spleen. 

Development 1282 

Relation 1282 

Structure 1283 



CONTENTS 



27 



SURFACE ANATOMY AND SURFACE MARKINGS. 



Surface Anatomy of the Head and Neck. 

The Bones 1287 

The Joints and Muscles 1288 

The Arteries . . , 1290 

Surface Markings of Special Regions of the Head 
and Neck. 

The Cranium 1291 

The Scalp 1291 

Bony Landmarks 1291 

The Brain • . . 1292 

Vessels 1294 

The Face 1294 

External Maxillary Artery .... 1294 

Trigeminal Nerve 1295 

Parotid Gland 1295 

The Nose 1296 

The Mouth 1296 

The Eye 1299 

The Ear 130C 

The Tympanic Antrum 1301 

The Neck 1301 

Muscles 1302 

Arteries 1302 

Veins 1303 

Nerves 1303 

Submaxillary Gland 1303 

Surface Anatomy of the Back. 

Bones 1303 

Muscles 1304 



Surface Markings of the Back. 

Bony Landmarks 1305 

Medulla Spinalis 1306 

Spinal Nerves 1307 

Surface Anatomy of the Thorax. 

Bones 1307 

Muscles 1307 

Mamma 1308 

Surface Markings of the Thorax. 

Bony Landmarks 1308 

Diaphragm 1309 

Surface Lines 1309 

Pleurae 1309 

Lungs 1310 

Trachea 1311 

Esophagus 1311 

Heart 1311 

Arteries 1312 

Veins 1312 

Surface Anatomy of the Abdomen. 

Skin 1313 

Bones 1313 

Muscles 1313 

Vessels 1313 

Viscera 1313 



Surface Markings of the Abdomen. 

Bony Landmarks 1315 

Muscles 1315 

Surface Lines 1315 

Stomach 1317 

Duodenum 1319 

Small Intestine 1319 

Cecum and Vermiform Process .... 1319 

Ascending Colon 1319 

Transverse Colon ' . . . 1319 

Descending Colon 1320 

IUac Colon 1320 

Liver • 1320 

Pancreas 1320 

Spleen 1320 

Kidneys 1320 

Ureters 1321 

Vessels 1321 

Nerves 1322 

Surface Anatomy of the Perineum. 

Skin 1322 

Bones 1322 

Muscles and Ligaments 1322 

Surface Markings of the Perineum. 

Rectum and Anal Canal 1322 

Male Urogenital Organs 1323 

Female Urogenital Organs 1323 

Surface Anatomy of the Upper Extremity. 

Skin 1325 

Bones 1326 

Articulations 1327 

Muscles 1327 

Arteries 1331 

Veins 1331 

Nerves "!.... 1331 

Surface Markings of the Upper Extremity. 

Bony Landmarks . . 1331 

Articulations 1331 

Muscles 1332 

Mucous Sheaths 1334 

Arteries 1334 

Nerves 1335 

Surface Anatomy of the Lower Extremity. 

Skin 1336 

Bones 1336 

Articulations 1338 

Muscles 1338 

Arteries 1341 

Veins 1342 

Nerves 1342 

Surface Markings of the Lower Extremity. 

Bony Landmarks 1342 

Articulations 1343 

Muscles 1343 

Mucous Sheaths 1343 

Arteries 1343 

Veins 1346 

Nerves 1346 



ANATOMICAL BIBLIOORAPHY 



INDEXES. 

Anatomical Bibliography of the Concilium Bibliographicum. 

Bibliographic Service; "Wistar Institute of Anatomy, 1917- 

Bibliographie Anatomique, 1893- 

Index Medicus, 1879- 

Index Catalogue of the Library of the Surgeon-General's Office, U. S. Army, 
1880- 

Jahresberichte iiber die Fortschritte der Anatomic und Physiologic, 1856-1894. 

Jahresberichte iiber die Fortschritte der Anatomic und Entwicklungsgeschichte, 
1895- 

JOURNALS. 

The Anatomical Record. 1906- 

The American Journal of Anatomy, 1901- 

Anatomische Hefte, 1892- 

Anatomischer Anzeiger, 1886- 

Archives d 'Anatomic IMicroscopique, 1897- 

Archiv fiir Anatomic und Physiologic, 1795- 

Archiv fiir Entwicklungsmechanik der Organismcn, 1894- 

Archiv fiir ^Nlicroskopische Anatomic, 1865- 

Archivo Italiano di Anatomia e di Embriologia, 1902- 

Biological Bulletin, 1900- 

Brain, 1878- 

Bibliographie Anatomique, 1893- 

Contributions to E^mbryology, Carnegie Institution of Washington, 1914— 

Comptcs Rendus de I'Association dcs Anatomistes, 1899- 

Gcgenbaur's ]\Iorphologisches Jahrbuch, 1876- 

International ]Monatsschrift fiir Anatomic und Histologic, 1884- 

The Journal of Anatomy and Physiology, 1867- 

Journal of Comparative Neurology, 1891- 

Journal de 1 'Anatomic et de Physiologic, etc., 1864- 

Journal of Experimental Zoology, 1904- 

Journal of ^Morphology, 1887- 

Le Nevraxe, 1900- 

Morphologische Arbeiten, 1892-1898. 

Petrus Camper Nederlandschc Bijdragen tot de Anatomic, 1902- 

Proceedings of the Royal Society, Series B. 

Quarterly Journal of ^Microscopical Science, 1853- 

Zeitschrift fiir ^Morphologic und Anthropologic, 1899- 

Zeitschrift fiir Wissenschaftliche Mikroskopie, 1884:- 

( xxviii) 



ANATOMY OF THE HUMAN BODY 



INTRODUCTION. 



THE term human anatomy comprises a consideration of the various structures 
which make up the human organism. In a restricted sense it deals merely 
with the parts which form the fully developed individual and which can be ren- 
dered evident to the naked eye by various methods of dissection. Regarded from 
such a standpoint it may be studied by two methods: (1) the various structures 
may be separately considered^ — systematic anatomy; or (2) the organs and tissues 
may be studied in relation to one another — topographical or regional anatomy. 

It is, however, of much advantage to add to the facts ascertained by naked- 
eye dissection those obtained by the use of the microscope. This introduces 
two fields of investigation, viz., the study of the minute structure of the various 
component parts of the body — ^histology — and the study of the human organism 
in its immature condition, i. e., the various stages of its intrauterine develop- 
ment from the fertilized ovum up to the period when it assumes an independent 
existence — embryology. Owing to the difficulty of obtaining material illustrating 
all the stages of this early development, gaps must be filled up by observations 
on the development of lower forms — comparative embryology, or by a consideration 
of adult forms in the line of human ancestry — comparative anatomy. The direct 
application of the facts of human anatomy to the various pathological conditions 
which may occur constitutes the subject of applied anatomy. Finally, the appre- 
ciation of structures on or immediately underlying the surface of the body is 
frequently made the subject of special study — surface anatomy. 

Systematic Anatomy.^ — ^The various systems of which the human body is 
composed are grouped under the following headings: 

1. Osteology — the bony system or skeleton. 

2. Syndesmology — the articulations or joints. 

3. Myology — the muscles. With the description of the muscles it is convenient 
to include that of the fasciae which are so intimately connected with them. 

4. Angiology — the vascular system, comprising the heart, bloodvessels, lymphatic 
vessels, and lymph glands. 

5. Neurology — the nervous system. The organs of sense may be included in 
this system. 

6. Splanchnology — the visceral system. Topographically the viscera form 
two groups, viz., the thoracic viscera and the abdomino-pelvic viscera. The 

heart, a thoracic viscus, is best considered with the vascular system. The rest 

3 ( 33 ) 



34 INTRODUCTION 

of the viscera may be grouped according to their functions: (a) the respiratory 
apparatus; (6) the digestive apparatus; and (c) the urogenital apparatus. Strictly 
speaking, the third subgroup should include only such components of the 
urogenital apparatus as are included within the abdomino-pelvic cavity, but it 
is convenient to study under this heading certain parts which lie in relation to 
the surface of the body, e. g., the testes and the external organs of generation. 

For descriptive purposes the body is supposed to be in the erect posture, with 
the arms hanging by the sides and the palms of the hands directed forward. The 
median plane is a vertical antero-posterior plane, passing through the center of the 
trunk. This plane will pass approximately through the sagittal suture of the skull, 
and hence any plane parallel to it is termed a sagittal plane. A vertical plane at 
right angles to the median plane passes, roughly speaking, through the central 
part of the coronal suture or through a line parallel to it; such a plane is known as 
a frontal plane or sometimes as a coronal plane. A plane at right angles to both 
the median and frontal planes is termed a transverse plane. 

The terms anterior or ventral, and posterior or dorsal, are employed to indicate 
the relation of parts to the front or back of the body or limbs, and the terms 
superior or cephalic, and inferior or caudal, to indicate the relative levels of different 
structures; structures nearer to or farther from the median plane are referred to as 
medial or lateral respectively. 

The terms superficial and deep are strictly confined to descriptions of the 
relative depth from the surface of the various structures; external and internal 
are reserved almost entirely for describing the Walls of cavities or of hollow 
viscera. In the case of the limbs the words proximal and distal refer to the 
relative distance from the attached end of the limb. 



EMBRYOLOGY. 



THE term Embryology, in its widest sense, is applied to the various changes 
which take place during the growth of an animal from the egg to the adult 
condition: it is, however, usually restricted to the phenomena which occur before 
birth. Embryology may be studied from two aspects: (1) that of ontogeny, which 
deals only with the development of the individual; and (2) that of phylogeny, 
which concerns itself with the evolutionary history of the animal kingdom. 

In vertebrate animals the development of a new being can only take place when 
a female germ cell or ovum has been fertilized by a male germ cell or spermatozoon. 
The ovum is a nucleated cell, and all tiie complicated changes by which the various 
tissues and organs of the body are formed from it, after it has been fertilized, are 
the result of two general processes, viz., segmentation and differentiation of cells. 
Thus, the fertilized ovum undergoes repeated segmentation into a number of cells 
which at first closely resemble one another, but are, sooner or later, differentiated 
into two groups: (1) somatic cells, the function of which is to build up the various 
tissues of the body; and (2) germinal cells, which become imbedded in the sexual 
glands — the ovaries in the female and the testes in the male — and are destined for 
the perpetuation of the species. 

Having regard to the main purpose of this work, it is impossible, in the space 
available in this section, to describe fully, or illustrate adequately, all the phenom- 
ena which occur in the different stages of the development of the human body. 
Only the principal facts are given, and the student is referred for further details 
to one or other of the text-books^ on human embryology. 

THE ANIMAL CELL. 

All the tissues and organs of the body originate from a microscopic structure 
(the fertilized ovum), which consists of a soft jelly-like material enclosed in a 
membrane and containing a vesicle or small spherical body inside which are one 
or more denser spots. This may be regarded as a complete cell. All the solid 
tissues consist largely of cells essentially similar to it in nature but differing in 
external form. 

In the higher organisms a cell may be defined as "a nucleated mass of proto- 
plasm of microscopic size." Its two essentials, therefore, are: a soft jelly-like 
material, similar to that found in the ovum, and usually styled cytoplasm, and a 
small spherical body imbedded in it, and termed a nucleus. Some of the unicellular 
protozoa contain no nuclei but granular particles which, like true nuclei, stain with 
basic dyes. The other constituents of the ovum, viz., its limiting membrane and 
the denser spot contained in the nucleus, called the nucleoliis, are not essential to 
the type cell, and in fact many cells exist without them. 

Cytoplasm (protoplasm) is a material probably of variable constitution during 
life, but yielding on its disintegration bodies chiefly of proteid nature. Lecithin 
and cholesterin are constantly found in it, as well as inorganic salts, chief among 

' Manual of Human Embryologj-, Keibel and Mall; Handbuch der vergleichenden und experimentellen Entwickel- 
uagslehre der Wirbeltiere, Oskar Hertwig; Lehrbuch der Entwickelungsgeschichte, Bonnet; The Physiology of 
Reproduction, Marshall. 

(35) 



36 



EMBRYOLOGY 



which are the phosphates and chlorides of potassium, sodium, and calcium. It is 
of a semifluid, viscid consistence, and probably colloidal in nature. The living 
CNtoplasm appears to consist of a homogeneous and structureless ground-substance 
in which are embedded granules of various t^-pes. The mitochondria are the most 
constant type of granule and vary in form from granules to rods and threads. 
Their fmiction is unknowTi. Some of the granules are proteid in nature and prob- 
ably essential constituents; others are fat, glycogen, or pigment granules, and are 
regarded as adventitious material taken in from without, and hence are styled 
cell-inclusions or paraplasm. ^Vhen, however, cells have been "fixed" by reagents 
a fibrillar or granular appearance can often be made out under a high power of the 
microscope. The fibrils are usually arranged in a network or reticulum, to which 
the term spongioplasm is applied, the clear substance in the meshes being termed 
hyaloplasm. The size and shape of the meshes of the spongioplasm vary in different 
cells and in different parts of the same cell. The relative amounts of spongioplasm 
and hyaloplasm also vary in different cells, the latter preponderating in the young 
cell and the former mcreasing at the expense of the hyaloplasm as the cell grows. 
Such appearances in fixed cells are no indication whatsoever of the existence of 



Cell wall 



Nuclear 
membrane 



Vacuole 




Centrosome consisting of cen- 
trospliere enclosing two cen- 
irioles 



Nucleolus 

Net-knot cf chromatin form- 
ing a pseudo-nucleolus 
Chromatin network 



Cell-inclusions {paraplasm) 



Fia. 1. — Diagram of a cell. (Modified from Wilson.) 



similar structures in the living, although there must have been something in the 
living cell to give rise to the fixed structures. The peripheral layer of a cell is in 
all cases modified, either by the formation of a definite cell membrane as in the ovum, 
or more frequently in the case of animal cells, by a transformation, probably 
chemical in nature, which is only recognizable by the fact that the surface of the 
cell behaves as a semipermeable membrane. 

Nucleus. — The nucleus is a minute body, imbedded in the protoplasm, and 
usually of a spherical or oval form, its size having little relation to that of the cell. 
It is surrounded by a well-defined wall, the nuclear membrane; this encloses the 
nuclear substance {iniclear matrix), which is composed of a homogeneous material 
in which is usually embedded one or two nucleoli. In fixed cells the nucleus seems 
to consist of a clear substance or karyoplasm and a network or karyomitome. The 
former is probably of the same nature as the hyaloplasm of the cell, but the latter, 
which forms also the wall of the nucleus, differs from the spongioplasm of the cell 
substance. It consists of fibers or filaments arranged in a reticular manner. These 
filaments are composed of a homogeneous material known as linin, which stains 
with acid dyes and contains embedded in its substance particles which have a 
strong affinity for basic dyes. These basophil granules have been named chromatin 



THE ANIMAL CELL 37 

or basichromatin and owe their staining properties to the presence of nucleic acid. 
Within the nuclear matrix are one or more highly refracting bodies, termed nucleoli, 
connected with the nuclear membrane by the nuclear filaments. They are regarded 
as being of two kinds. Some are mere local condensations ("net-knots") of the 
chromatin; these are irregular in shape and are termed pseudo-nucleoli ; others are 
distinct bodies differing from the pseudo-nucleoli both in nature and chemical 
composition; they may be termed true nucleoli, and are usually found in resting 
cells. The true nucleoli are oxyphil, i. e., they stain with acid dyes. 

]\Iost living cells contain, in addition to their protoplasm and nucleus, a small 
particle which usually lies near the nucleus and is termed the centrosome. In the 
middle of the centrosome is a minute body called the centriole, and surrounding this 
is a clear spherical mass known as the centrosphere. The protoplasm surround- 
ing the centrosphere is frequently arranged in radiating fibrillar rows of granules, 
forming what is termed the attraction sphere. 

Reproduction of Cells. — Reproduction of cells is effected either by direct or by 
indirect division. In reproduction by direct division the nucleus becomes constricted 
in its center, assuming an hour-glass shape, and then divides into two. This is fol- 
lowed by a cleavage or division of the whole protoplasmic mass of the cell; and thus 
two daughter cells are formed, each containing a nucleus. These daughter cells are 
at first smaller than the original mother cell; but they grow, and the process 
may be repeated in them, so that multiplication may take place rapidly. Indirect 
divsion or karyokinesis (karyomitosis) has been observed in all the tissues — genera- 
tive cells, epithelial tissue, connective tissue, muscular tissue, and nerve tissue. 
It is possible that cell division may always take place by the indirect method. 

The process of indirect cell division is characterized by a series of complex 
changes in the nucleus, leading to its subdivision; this is followed by cleavage 
of the cell protoplasm. Starting with the nucleus in the quiescent or resting stage, 
these changes may be briefly grouped under the four following phases (Fig. 2). 

1. Prophase. — The nuclear network of chromatin filaments assumes the form 
of a twisted skein or spirem, while the nuclear membrane and nucleolus disappear. 
The convoluted skein of chromatin divides into a definite number of V-shaped 
segments or chromosomes. The number of chromosomes varies in different animals, 
but is constant for all the cells in an animal of any given species; in man the number 
is given by Flemming and Duesberg as twenty-four.^ Coincidently with or pre- 
ceding these changes the centriole, which usually lies by the side of the nucleus, 
undergoes subdivision, and the two resulting centrioles, each surrounded by a 
centrosphere, are seen to be connected by a spindle of delicate achromatic fibers 
the achromatic spindle. The centrioles move away from each other — one toward 
either extremity of the nucleus — and the fibrils of the achromatic spindle are cor- 
respondingly lengthened. A line encircling the spindle midway between its ex- 
tremities or poles is named the equator, and around this the V-shaped chromosomes 
arrange themselves in the form of a star, thus constituting the mother star or 
monaster. 

2. Metaphase. — Each V-shaped chromosome now undergoes longitudinal 
cleavage into two equal parts or daughter chromosomes, the cleavage commencing 
at the apex of the V and extending along its divergent limbs. 

3. Anaphase. — The daughter chromosomes, thus separated, travel in opposite 
directions along the fibrils of the aclu'omatic spindle toward the centrioles, around 
which they group themselves, and thus two star-like figures are formed, one at 
either pole of the achromatic spindle. This constitutes the diaster. The daughter 
chromosomes now arrange themselves into a skein or spirem, and eventually form 
the network of chromatin which is characteristic of the resting nucleus. 

Dr. J. Duesberg, Anat. Anz., Band xxviii, S. 475. 



38 



EMBRYOLOGY 



4. Telophase. — The cell protoplasm begins to appear constricted around the 
equator of the achromatic spindle, where double rows of granules are also sometimes 
seen. The constriction deepens and the original cell gradually becomes divided 
into two new cells, each with its owii nucleus and centrosome, which assume the 
ordinary positions occupied by such structures in the resting stage. The nuclear 
membrane and nucleolus are also differentiated during this phase. 







II 






VI 




VII 



VIII 




I "i<f] 





^^^- 2-.— Diagram showing the changes which occur in the centrosomes and nucleus of a cell in the process of mitotic 
division, (bchafer.) / to ///, prophase; IV, metaphase; V and VI, anaphase; VII and VIII. telophase. 



THE OVUM. 

The ova are developed from the primitive germ cells which are imbedded in 
the^ substance of the ovaries. Each primitive germ cell gives rise, by repeated 
divisions, to a number of smaller cells termed obgonia, from which the ova or 
primary oocjrtes are developed. 

Human ova are extremely minute, measuring about 0.2 mm. in diameter, and 
are enclosed within the egg follicles of the ovaries; as a rule each follicle contains 



THE OVUM 



39 



a single ovum, but sometimes two or more are present.^ By the enlargement and 
subsequent rupture of a follicle at the surface of the ovary, an ovum is liberated and 
conveyed by the uterine tube to the cavity of the uterus. Unless it be fertilized 
it undergoes no further development and is discharged from the uterus, but if 
fertilization take place it is retained within the uterus and is developed into a 
new being. 

In appearance and structure the ovum (Fig. 3) differs little from an ordinary 
cell, but distinctive names have been applied to its several parts; thus; the cell 
substance is known as the yolk or ooplasm, the nucleus as the germinal vesicle, and 
the nucleolus as the germinal spot. The ovum is enclosed within a thick, trans- 




FiG. 3. — Human ovum examined fresh in the liquor folliculi. (Waldeyer.) The zona pellucida is seen aa a thick 
clear girdle surrounded by the cells of the corona radiata. The egg itself shows a central granular deutoplasmie area 
and a peripheral clear layer, and encloses the germinal vesicle, in which is seen the germinal spot. 

parent envelope, the zona striata or zona pellucida, adhering to the outer surface 
of which are several layers of cells, derived from those of the follicle and collectively 
constituting the corona radiata. 

Yolk. — The yolk comprises (1) the cytoplasm of the ordinary animal cell with its 
spongioplasm and hyaloplasm; this is frequently termed the formative yolk; (2) 
the nutritive yolk or deutoplasm, which consists of numerous rounded granules of 
fatty and albuminoid substances imbedded in the cytoplasm. In the mammalian 
ovum the nutritive volk is extremelv small in amount, and is of service in nourish- 



See description of the ovary on a future page. 



40 EMBRYOLOGY 

ing the embryo in the early stages of its development only, whereas in the egg 
of the bird there is sufficient to supply the chick with nutriment throughout 
the whole period of incubation. The nutritive yolk not only varies in amount, 
but in its mode of distribution within the egg; thus, in some animals it is almost 
uniformly distributed throughout the cytoplasm; in some it is centrally placed and 
is surrounded by the cytoplasm; in others it is accumulated at the lower pole of the 
ovum, while the cytoplasm occupies the upper pole. A centrosome and centriole 
are present and lie in the immediate neighborhood of the nucleus. 

Germinal Vesicle. — The germinal vesicle or nucleus is a large spherical body 
which at first occupies a nearh' central position, but becomes eccentric as the growth 
of the ovum proceeds. Its structure is that of an ordinary cell-nucleus, viz., it 
consists of a reticulum or karyomitome, the meshes of which are filled with 
karyoplasm, while connected with, or imbedded in, the reticulum are a number 
of chromatin masses or chromosomes, which may present the appearance of a 
skein or may assume the form of rods or loops. The nucleus is enclosed by a 
delicate nuclear membrane, and contains in its interior a well-defined nucleolus 
or germinal spot. 

Coverings of the Ovum.^ — The zona striata or zona pellucida (Fig. 3) is a thick 
membrane, which, under the higher powers of the microscope, is seen to be radially 
striated. It persists for some time after fertilization has occurred, and may serve 
for protection during the earlier stages of segmentation. It is not yet determined 
whether the zona striata is a product of the cytoplasm of the ovum or of the cells 
of the corona radiata, or both. 

The corona radiata (Fig. 3) consists or two or three strata of cells; they are 
derived from the cells of the follicle, and adhere to the outer surface of the zona 
striata when the ovum is set free from the follicle; the cells are radially arranged 
around the zona, those of the innermost layer being columnar in shape. The 
cells of the corona radiata soon disappear; in some animals they secrete, or 
are replaced by, a layer of adhesive protein, which may assist in protecting and 
nourishing the ovum. 

The phenomena attending the discharge of the ova from the follicles belong 
more to the ordinary functions of the ovary than to the general subject of embry- 
ology, and are therefore described with the anatomy of the ovaries.^ 

Maturation of the Ovum. — Before an ovum can be fertilized it must undergo 
a process of maturation or ripening. This takes place previous to or immediately 
after its escape from the follicle, and consists essentially of an unequal subdivision 
of the ovum (Fig. 4) first into two and then into four cells. Three of the four 
cells are small, incapable of further development, and are termed polar bodies or 
polocytes, while the fourth is large, and constitutes the mature ovum. The process 
of maturation has not been observed in the human ovum, but has been carefully 
studied in the ova of some of the lower animals, to which the following description 
applies. 

It was pointed out on page 37 that the number of chromosomes found in the 
nucleus is constant for all the cells in an animal of any given species, and that in 
man the number is probably twenty-four. This applies not only to the somatic 
cells but to the primitive ova and their descendants. For the purpose of illustrating 
the process of maturation a species may be taken in which the number of nuclear 
chromosomes is four (Fig. 5). If an ovum from such be observed at the beginning 
of the maturation process it will be seen that the number of its chromosomes is 
apparently reduced to two. In reality, however, the number is doubled, since 
each chromosome consists of four granules grouped to form a tetrad. During the 
metaphase (see page 37) each tetrad divides into two dyads, which are equally 

' See description of the ovary on a future page. 



THE OVUM 



41 



distributed between the nuclei of the two cells formed by the first division of the 
ovum. One of the cells is almost as large as the original ovum, and is named 
the secondary oocyte; the other is small, and is termed the first polar body. The 




fpn 



F:g. 4. — Formation of polar bodies in Asterias glacialis. (Slightly modified from Hertwig.) In I the polar spindle 
(sp) has advanced to the surface of the egg. In // a small elevation (ph') is formed which receives half of the spindle. 
In /// the elevation is constricted ofT, forming the first polar body (p6'), and a second spindle is formed. In IV is 
seen a second elevation which in T' has been constricted off as the second polar body (pt>'). Out of the remainder of 
the spindle (/.p't in VI) the female pronucleus is developed. 

secondary oocyte now undergoes subdivision, during which each dyad divides and 
contributes a single chromosome to the nucleus of each of the two resulting cells. 



Primary oocyte 



Primary oocyte 
(comtnencing 
maturation) 




Secondary 
oocyte 



¥ \ First j>oUr 
body 



Mature 
ovum 



Polar bodies 
Fig. 5. — Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum. 



This second division is also unequal, producing a large cell which constitutes the 
mature ovum, and a small cell, the second polar body. The first polar body fre- 
quently divides while the second is being formed, and as a final result four cells 



42 



EMBRYOLOGY 



are produced, viz., the ^mature ovum and three polar bodies, each of which con- 
tains two chromosomes, i. e., one-half the number present in the nuclei of the 
somatic cells of members of the same species. The nucleus of the mature ovum 
is termed the female pronucleus. 

THE SPERMATOZOON. 

The spermatozoa or male germ cells are developed in the testes and are present 
in enormous numbers in the seminal fluid. Each consists of a small but greatly 
modified cell. The human spermatozoon possesses a head, a neck, a connecting 
piece or body, and a tail (Fig. 6). 



Head 



Connecting 'piece 




'Perforator 



) yeck 



Tail'. 



End-piece 




y Head-cap 



Anterior centriole 
Posterior centriole 



•Spiral thread 
'Mitochondria sheath 



•Terminal disc 



■Axial filament 



Fig. 6. — Human spermatozoon. Diagrammatic. A. Surface view. B. Profile ^^ew. In C the head, neck, 

and connecting piece are more highly magnified. 

The head is oval or elliptical, but flattened, so that when viewed in profile 
it is pear-shaped. Its anterior two-thirds are covered by a layer of modified proto- 
plasm, which is named the head-cap. This, in some animals, e. g., the salamander, 
is prolonged into a barbed spear-like process or perforator, which probabl}^ facilitates 
the entrance of the spermatozoon into the ovum. The posterior part of the head 
exhibits an affinity for certain reagents, and presents a transversely striated appear- 
ance, being crossed by three or four dark bands. In some animals a central rod- 
like filament extends forward for about two-thirds of the length of the head, while 
in others a rounded body is seen near its center. The head contains a mass of 



THE SPERMATOZOON 43 

chromatin, and is generally regarded as the nucleus of the cell surrounded by a 
thin envelope. 

The neck is less constricted in the human spermatozoon than in those of some 
of the lower animals. The anterior centriole, represented by two or three rounded 
particles, is situated at the junction of the head and neck, and behind it is a band 
of homogeneous substance. 

The connecting piece or body is rod-like, and is limited behind by a terminal 
disk. The posterior centriole is placed at the junction of the body and neck and, 
like the anterior, consists of two or three rounded particles. From this centriole 
an axial filament, surrounded by a sheath, runs backward through the body and 
tail. In the body the sheath of the axial filament is encircled by a spiral thread, 
around which is an envelope containing mitochondria granules, and termed the 
mitochondria sheath. 

The tail is of great length, and consists of the axial thread or filament, sur- 
rounded by its sheath, which may contain a spiral thread or may present a striated 
appearance. The terminal portion or end-piece of the tail consists of the axial 
filament only. 



Primary cocyie Primary spermatocyte 



Mature 
ovum 





Secondary f^ r-\ (^ f\ Secondary 

oocyte v. J \^ K J V J spermatocytes 





0_^0JD 0_0_0_0 

Polar bodies Spermatids 

Fig. 7. — Scheme showing analogies in the process of maturation of the ovum and the development of the spermatids 

(young spermatozoa). 

Krause gives the length of the human spermatozoon as between 52fj. and 62/^, 
the head measuring 4 to 5/x, the connecting piece 6/x, and the tail from 41 /x to 52 /x. 

By virtue of their tails, which act as propellers, the spermatozoa are capable of 
free movement, and if placed in favorable surroundings, e. g., in the female pas- 
sages, will retain their vitality and power of fertilizing for several days. In certain 
animals, e. g., bats, it has been proved that spermatozoa retained in the female 
passages for several months are capable of fertilizing. 

The spermatozoa are developed from the primitive germ cells which have become 
imbedded in the testes, and the stages of their development are very similar to those 
of the maturation of the ovum. The primary germ cells undergo division and 
produce a number of cells termed spermatogonia, and from these the primary 
spermatocytes are derived. Each primary spermatocyte divides into two secondary 
spermatocytes, and each secondary spermatocyte into two spermatids or young 
spermatozoa; from this it will be seen that a primary spermatocyte gives rise to 
jour spermatozoa. On comparing this process with that of the maturation of the 
ovum (Fig. 7) it will be observed that the primary spermatocyte gives rise to 
two cells, the secondary spermatocytes, and the primary oocyte to two cells, the 
secondary oocyte and the first polar body. Again, the two secondary sperma- 



44 



EMBRYOLOGY 



tocytes by their subdivision give origin to four spermatozoa, and the secondary 
oocyte and first polar body to four cells, the mature ovum and three polar bodies. 
In the development of the spermatozoa, as in the maturation of the ovum, there 
is a reduction of the nuclear chromosomes to one-half of those present in the 
primary spermatocyte. But here the similarity ends, for it must be noted that 
the four spermatozoa are of equal size, and each is capable of fertilizing a mature 
ovum, whereas the three polar bodies are not only very much smaller than the 
mature ovum but are incapable of further development, and may be regarded as 
abortive ova. 

FERTILIZATION OF THE OVUM. 

Fertilization consists in the union of the spermatozoon with the mature ovum 
(Fig. 8). Nothing is known regarding the fertilization of the human ovum, but 



1. Polar hod 
Female 'pronucleus 

Male pronucleus 




Female pronucleus 
Male pronucleus 



Segmentation 
nucleus 





Female pronucleus 
Male pronucleus 



4. 



Fused pronuclei 



Segmentation 

nucleus 
commencing 
division) 



Fig. 8. — The process of fertilization in the ovum of a mouse. (After Sobotta.) 

the various stages of the process have been studied in other mammals, and from 
the knowledge so obtained it is believed that fertilization of the human ovum takes 
place in the lateral or ampullary part of the uterine tube, and the ovum is then 
conveyed along the tube to the cavity of the uterus — a journey probably occupy- 
ing seven or eight days and during which the ovum loses its corona radiata and zona 
striata and undergoes segmentation. Sometimes the fertilized ovum is arrested 
in the uterine tube, and there undergoes development, giving rise to a tubal preg- 
nancy; or it may fall into the abdominal cavity and produce an abdominal preg- 
nancy. Occasionally the ovum is not expelled from the follicle when the latter 
ruptures, but is fertilized within the follicle and produces what is known as an 
ovarian pregnancy. Under normal conditions only one spermatozoon enters the 
yolk and takes part in the process of fertilization. At the point where the sperma 



SEGMENTATION OF THE FERTILIZED OVUM 



45 



tozoon is about to pierce, the yolk is drawn out into a conical elevation, termed 
the cone of attraction. As soon as the spermatozoon has entered the yolk, the per- 
ipheral portion of the latter is transformed into a membrane, the vitelline membrane 
which prevents the passage of additional spermatozoa. Occasionally a second 
spermatozoon may enter the yolk, thus giving rise to a condition of polyspermy: 
when this occurs the ovum usually develops in an abnormal manner and gives rise 
to a monstrosity. Having pierced the yolk, the spermatozoon loses its tail, while 
its head and connecting piece assume the form of a nucleus containing a cluster of 
chromosomes. This constitutes the male pronucleus, and associated with it there are 
a centriole and centrosome. The male pronucleus passes more deeply into the yolk, 
and coincidently with this the granules of the cytoplasm surrounding it become 
radially arranged. The male and female pronuclei migrate toward each other, and. 
meeting near the center of the yolk, fuse to form a new nucleus, the segmentation 
nucleus, which therefore contains both male and female nuclear substance; the 
former transmits the individualities of the male ancestors, the latter those of the 
female ancestors, to the future embryo. By the union of the male and female 
pronuclei the number of chromosomes is restored to that which is present in the 
nuclei of the somatic cells. 




FiQ. 9. — First stages of segmentation of a mammalian ovum. Semidiagrammatic. (From a drawing by Alien 
Tiiomson.) z.p. Zona striata, p.gl. Polar bodies, a. Two-cell stage, b. Four-cell stage, c. Eight-cell stage. 
d, e. Morula stage. 

SEGMENTATION OF THE FERTILIZED OVUM. 

The early segmentation of the human ovum has not yet been observed, but 
judging from what is known to occur in other mammals it may be regarded as 
certain that the process starts immediately after the ovum has been fertilized, 
i. e., while the ovum is in the uterine tube. The segmentation nucleus exhibits 
the usual mitotic changes, and these are succeeded by a division of the ovum into 
two cells of nearly equal size.^ The process is repeated again and again, so that 



' In the mammalian ova the nutritive yolk or deutoplasm is small in amount and uniformly distributed through- 
out the cytoplasm; such ova undergo complete division during the process of segmentation, and are therefore termed 
holoblastic. In the ova of birds, reptiles, and fishes where the nutritive yolk forms by far the larger portion of the 
egg, the cleavage is limited to the formative yolk, and is therefore only partial; such ova are termed meroblastic._ Again, 
it has been observed, in some of the lower animals, that the pronuclei do not fuse but merely lie in apposition. At 
the commencement of the segmentation process the chromosomes of the two pronuclei group themselves around the 
equator of the nuclear spindle and then divide; an equal number of male and female chromosomes travel to the opposite 
poles of the spindle, and thus the male and female pronuclei contribute equal shares of chromatin to the nuclei of 
the two cells which result from the subdivision of the fertilized ovum. 



46 



EMBRYOLOGY 



the two cells are succeeded by four, eight, sixteen, thirty-two, and so on, with the 
result that a mass of cells is found within the zona striata, and to this mass the term 
morula is applied (Fig. 9). The segmentation of the mammalian ovum may not 
take place in the regular sequence of two, four, eight, etc., since one of the two first 
formed cells may subdivide more rapidly than the other, giving rise to a three- 
or a five-cell stage. The cells of the morula are at first closely aggregated, but soon 
they become arranged into an outer or peripheral layer, the trophoblast, which 



Inner cell-mass 

Entoderm 



Blastodermic vesicle 
\ 



Trophoblast 




Fig. 10. — Blastodermic vesicle of Vespertilio murinus. (After van Beneden. 
• Inner cell-mass Trofhoblast 




Embryonic ectoderm Entoderm 
Fig. 11. — Section through embryonic disk of Vespertilio murinus. (After van Beneden.) 



Maternal bloodvessels 



Amniotic cavity 



Syncytiotro'phohlost 
Cytotrophdblast 




Embryonic ectoderm Entoderm 

Fig. 12. — Section through embryonic area of Vespertilio murinus to show the formation of the amniotic cavity. 

(After van Beneden,) 

does not contribute to the formation of the embryo proper, and an inner cell-mass, 
from which the embryo is developed. Fluid collects between the trophoblast 
and the greater part of the inner cell-mass, and thus the morula is converted into 
a vesicle, the blastodermic vesicle (Fig. 10). The inner cell-mass remains in con- 
tact, however, with the trophoblast at one pole of the ovum; this is named the 
embryonic pole, since it indicates the situation where the future embryo will be 
developed. The cells of the trophoblast become differentiated into two strata: an 



SEGMENTATION OF THE FERTILIZED OVUM 47 

outer, termed the syncytium or syncytiotrophoblast, so named because it consists of 
a layer of protoplasm studded with nuclei, but showing no evidence of subdivision 
into cells; and an inner la^er, the cytotrophoblast or layer of Langhans, in which 
the cell outlines are defined. As already stated, the cells of the trophoblast do not 
contribute to the formation of the embryo proper; they form the ectoderm of the 
chorion and play an important part in the development of the placenta. On the 
deep surface of the inner cell-mass a layer of flattened cells, the entoderm, is differ- 
entiated and quickly assumes the form of a small sac, the yolk-sac. Spaces appear 
between the remaining cells of the mass (Fig. 11), and by the enlargement and 
coalescence of these spaces a cavity, termed the amniotic cavity (Fig. 12), is gradually 
developed. The floor of this cavity is formed by the embryonic disk composed 
of a layer of prismatic cells, the embryonic ectoderm, derived from the inner cell- 
mass and lying in apposition with the entoderm. 

The Primitive Streak; rormation of the Mesoderm. — The embryonic disk 
becomes oval and then pear-shaped, the wider end being directed forward. Near 
the narrow, posterior end an opaque streak, the primitive 
streak (Figs. 13 and 14), makes its appearance and extends 
along the middle of the disk for about one-half of its 
length; at the anterior end of the streak there is a knob- 
like thickening termed Hensen's knot. A shallow groove, 
the primitive groove, appears on the surface of the streak, 
and the anterior end of this groove communicates by 
means of an aperture, the blastophore, with the yolk-sac. 
The primitive streak is produced by a thickening of the 
axial part of the ectoderm, the cells of which multiply, 
grow downward, and blend with those of the subjacent 
entoderm (I'ig. 15). From the sides of the primitive streak ^ ,o ^ . 

,.,,°„,, , ^ , ■, Fig. 13. — Surface view of 

a third la^'er ot cells, the mesoderm, extends lateralward embryo of a rabbit. (After 

1 , ,1^ ,1 1.1 .1 1 1 1 i> Kolliker.) arg. Embryonic 

between the ectoderm and entoderm; the caudal end ot disk. pr. Primitive streak. 
the primitive streak forms the cloacal membrane. 

The extension of the mesoderm takes place throughout the whole of the embry- 
onic and extra-embryonic areas of the ovum, except in certain regions. One of 
these is seen immediately in front of the neural tube. Here the mesoderm extends 
forward in the form of two crescentic masses, which meet in the middle line so as 
to enclose behind them an area which is devoid of mesoderm. Over this area the 
ectoderm and entoderm come into direct contact with each other and constitute 
a thin membrane, the buccopharyngeal membrane, which forms a septum between 
the primitive mouth and pharynx. In front of the buccopharyngeal area, where 
the lateral crescents of mesoderm fuse in the middle line, the pericardium is 
afterward developed, and this region is therefore designated the pericardial area. A 
second region where the mesoderm is absent, at least for a time, is that imme- 
diately in front of the pericardial area. This is termed the proamniotic area, and 
is the region where the proamnion is developed; in man, however, a proamnion is 
apparently never formed. A third region is at the hind end of the embryo where 
the ectoderm and entoderm come into apposition and form the cloacal membrane. 

The blastoderm now consists of three layers, named from without inward: 
ectoderm, mesoderm, and entoderm; each has distinctive characteristics and gives 
rise to certain tissues of the body.^ 

Ectoderm. — The ectoderm consists of columnar cells, which are, however, somewhat 
flattened or cubical toward the margin of the embryonic disk. It forms the whole 
of the nervous system, the epidermis of the skin, the lining cells of the sebaceous, 

' The mode of formation of the germ layers in the human ovum has not yet been observed ; In the youngest known 
human ovum (viz., that described by Bryce and Teacher), all three layers are already present and the mesoderm is 
split into its two layers. The extra-embr>-onic celom is of considerable size, and scattered mesodermal strands are 
seen stretching between the mesoderm of the yolk-sac and that of the chorion. 




48 



EMBRYOLOGY 
Yolk-sac 




Notochord 



Amnion 



\\ 



Allantois in body-stalk 




— Amnion 



Neurenteric canal 



Primitive streak 



Fig. 14.— Surface view of embryo of Hylobates concolor. (After Selenka.) The amnion has been opened to expose 

the embryonic disk. 




^^ife'^5m 




Fig. 15. — Series of transverse sections through the embrj'onic disk of Tarsius. (After Hubrecht ) Section I passes 
through the disk, in front of Hansen's knot and sliows only the ectoderm and entoderm. Sections//,///, and /Fpass 
through Hensen's knot, which is seen in V tapering away into the primitive streak. In ///, IV , and V the mesoderm 
is seen springing from the keel-like thickening of the ectoderm, which in /// and IV is observed to be continuous into 
"the entoderm. 



SEGMENTATION OF THE FERTILIZED OVUM 



49 



sudoriferous, and mammary glands, the hairs and nails, the epithelium of the nose 
and adjacent air sinuses, and that of the cheeks and roof of the mouth. From it 
also are derived the enamel of the teeth, and the anterior lobe of the hypophysis 
cerebri, the epithelium of the cornea, conjunctiva, and lacrimal glands, and the 
neuro-epithelium of the sense organs. 

Entoderm.— The entoderm consists at first of flattened cells, which subsequently 
become columnar. It forms the epithelial lining of the whole of the digestive tube 
excepting part of the mouth and pharynx and the terminal part of the rectum 
(which are lined by involutions of the ectoderm), the lining cells of all the glands 
which open into the digestive tube, including those of the liver and pancreas. 




m. 



IV, 






- sm 









mty 



-'f^//j 



, •* # »• •••••■ • ••- 



••■•••44 



ta^ 



'%% 



:•:*','' /i^siTf --/=?='• 



Fig. 16. — A series of transverse sections through an embryo of the dog. (After Bonnet.) Section / is the most 
anterior. In V the neural plate is spread out nearly flat. The series shows the uprising of the neural folds to form the 
neural canal, a. Aortae. c. Intermediate cell mass. ect. Ectoderm. e7il. Entoderm, h, h. Rudiments of endothelial 
heart tubes. In ///, IV, and V the scattered cells represented between the entoderm and splanchnic layer of meso- 
derm are the vasoformative cells which give origin in front, according to Bonnet, to the heart tubes, h; l.p. Lateral 
plate still undivided in /, II, and III; in IV and V split into somatic (sm) and splanchnic (sp) layers of mesoderm. 
Tnes. Mesoderm, p. Pericardium, so. Primitive segment. 

the epithelium of the auditory tube and tympanic cavity, of the trachea, bronchi, 
and air cells of the lungs, of the urinary bladder and part of the urethra, and that 
which lines the follicles of the thyroid gland and thymus. 

Mesoderm. — The mesoderm consists of loosely arranged branched cells sur- 
rounded by a considerable amount of intercellular fluid. From it the remaining 
tissues of the body are developed. The endothelial lining of the heart and blood- 
vessels and the blood corpuscles are, however, regarded by some as being of ento- 
dermal origin. 

As the mesoderm develops between the ectoderm and entoderm it is separated 
into lateral halves by the neural tube and notochord, presently to be described. A 
4 



50 



EMBRYOLOGY 



longitudinal groove appears on the dorsal surface of either half and divides it into 
a medial column, the paraxial mesoderm, lying on the side of the neural tube, and 
a lateral portion, the lateral mesoderm. The mesoderm in the floor of the groove 
connects the paraxial with the lateral mesoderm and is known as the intermediate 
cell-mass; in it the genito-urinary organs are developed. The lateral mesoderm 
splits into two layers, an outer or somatic, which becomes applied to the inner surface 
of the ectoderm, and with it forms the somatopleure ; and an inner or splanchnic, 
which adheres to the entoderm, and with it forms the splanchnopleure (Fig. IG). 
The space between the two layers of the lateral mesoderm is termed the celom. 

THE NEURAL GROOVE AND TUBE. 

In front of the primitive streak two longitudinal ridges, caused by a folding up 
of the ectoderm, make their appearance, one on either side of the middle line 
(Fig. 16). These are named the neural folds; they commence some little distance 



Yolk-sac 



Amnion 



Neural groove 



Neurenteric canal 



Primitive streak 




Body-stalk -z 



Fig. 17. — Human embryo — length, 2 mm. Dorsal view, with the amnion laid open. X 30. (After Graf Spee.) 



behind the anterior end of the embryonic disk, w^here they are continuous with 
each other, and from there gradually extend backward, one on either side of the 
anterior end of the primitive streak. Between these folds is a shallow median 
groove, the neural groove (Figs. 10, 17) . The groove gradually deepens as the neural 
folds become elevated, and ultimately the folds meet and coalesce in the middle line 
and convert the groove into a closed tube, the neural tube or canal (Fig. 18), the 
ectodermal wall of which forms the rudiment of the nervous system. After the 
coalescence of the neural folds over the anterior end of the primitive streak, the 
blastopore no longer opens on the surface but into the closed canal of the neural 
tube, and thus a transitory communication, the neurenteric canal, is established 
between the neural tube and the primitive digestive tube. The coalescence of the 
neural folds occurs first in the region of the hind-brain, and from there extends 
forward and backward; toward the end of the third week the front opening (anterior 
neuropore) of the tube finally closes at the anterior end of the future brain, and 
forms a recess which is in contact, for a time, with the overlying ectoderm; the 
hinder part of the neural groove presents for a time a rhomboidal shape, and to this 



THE NEURAL GROOVE AND TUBE 



51 



expanded portion the term sinus rhomboidalis has been applied (Fig. 18). Before 
the neural groove is closed a ridge of ectodermal cells appears along the prominent 
margin of each neural fold ; this is termed the neural crest or ganglion ridge, and from 
it the spinal and cranial nerve ganglia and the ganglia of the sympathetic nervous 
system are developed. By the upward growth of the mesoderm the neural tube 
is ultimately separated from the overlying ectoderm. 



Head fold of amnion partly 
covering the fore-brain 



Mid-hrain 



Hind-brain -i-^ 



Nerve ganglion 



Auditory vesicle -K^ - i 



Vitelline vein 



Fourteenth primitive 
segment 



Paraxial mesoderm 



Neural fold 




Heart 



Sinus rhomboidalis -^ 



Remains of primitive streak ^ 



Fig. 18. — Chick embryo of thirty-three hour.'i' incubation, vieucJ liuin the dorsal aspect. X 30. 

(From Duval'3 "Atlas d'Embryologie.") 



The cephalic end of the neural groove exhibits several dilatations, which, when 
the tube is closed, assume the form of three vesicles; these constitute the three 
primary cerebral vesicles, and correspond respectively to the future fore-brain (pros- 
enceyhalon) , mid-brain (mesencephalon), and hind-brain {rhombencephalon) (Fig. 
18). The walls of the vesicles are developed into the nervous tissue and neuroglia 
of the brain, and their cavities are modified to form its ventricles. The remainder 



52 



EMBRYOLOGY 



of the tube forms the medulla spinalis or spinal cord; from its ectodermal wall 
the nervous and neuroglial elements of the medulla spinalis are developed while 
the cavity persists as the central canal. 



THE NOTOCHORD. 

The notochord (Fig. 19) consists of a rod of cells situated on the ventral aspect 
of the neural tube; it constitutes the foundation of the axial skeleton, since around 
it the segments of the vertebral column are formed. Its appearance synchronizes 
with that of the neural tube. On the ventral aspect of the neural groove an axial 
thickening of the entoderm takes place; this thickening assumes the appearance 
of a furrow — the chordal furrow^ — the margins of which come into contact, and so 
convert it into a solid rod of cells — the notochord — which is then separated from 
the entoderm. It extends throughout the entire length of the future vertebral 



Ectoderm ., 



Neural canal Primitive Wolffian 

segment duct Celom 

, f 



Somatic mesoderm 



Entoderm ''' 




Notochord Aorta Splanchnic mesoderm 

Fig. 19. — Transverse section of a c}iick embryo of forty-five hours' incubation. 



(Balfour.) 



column, and reaches as far as the anterior end of the mid-brain, where it ends in 
a hook-like extremity in the region of the future dorsum sellse of the sphenoid 
bone. It lies at first between the neural tube and the entoderm of the yolk-sac, 
but soon becomes separated from them by the mesoderm, which grows medial- 
ward and surrounds it. From the mesoderm 
surrounding the neural tube and notochord, 
the skull and vertebral column, and the 
membranes of the brain and medulla spinalis 
are developed. 

. THE PRIMITIVE SEGMENTS. 



Toward the end of the second week 
transverse segmentation of the paraxial 
mesoderm begins, and it is converted into 
a series of well-defined, more or less cubical 
masses, the primitive segments (Figs. IS, 
19, 20), which occupy the entire length of 
the trunk on either side of the middle line 
from the occipital region of the head. Fach 
segment contains a central cavity — myocoel 
— which, however, is soon filled with angular 
and spindle-shaped cells. 

The primitive segments lie immediately 
under the ectoderm on the lateral aspect of 
the neural tube and notochord, and are con- 
nected to the lateral mesoderm by the inter- 
mediate cell-mass. Those of the trunk mav 




Yolk- 



sac 



Cut edge of amnion 
Primitive segments 



Fig 



— Neural folds 



•'^'■^37^ • Neurenteric canal 



-Dorsum of human embryo, 2.11 mm. 
length. (After Eternod.) 



SEPARATION OF THE EMBRYO 



53 



be arranged in the following groups, viz.: cervical 8, thoracic 12, lumbar 5, 
sacral 5, and coccygeal from 5 to 8. Those of the occipital region of the head 
are usually described as being four in number. In mammals primitive segments 
of the head can be recognized only in the occipital region, but a study of the 
lower vertebrates leads to the belief that they are present also in the anterior 
part of the head, and that altogether nine segments are represented in the 
cephalic region. 

SEPARATION OF THE EMBRYO. 

The embryo increases rapidly in size, but the circumference of the embryonic 
disk, or line of meeting of the embryonic and amniotic parts of the ectoderm, is of 
relatively glow growth and gradually comes to form a constriction between the 
embryo and the greater part of the yolk-sac. By means of this constriction, which 
corresponds to the future umbilicus, a small part of the yolk-sac is enclosed within 
the embryo and constitutes the primitive digestive tube. 



Villi of chorion 



Amnion 
Embryonic disk 



Rvdiment of heart 




Chorion 

-.vigs^- ^ Mesoderm 

Body-stalk 
Primitive streak 

Allantois 



Entoderm 



Mesoderm 



Bloodvessel 



Fig. 21. — Section through the embryo which ia represented in Fig. 17. (After Graf Spee.) 



The embryo increases more rapidly in length than in width, and its cephalic and 
caudal ends soon extend beyond the corresponding parts of the circumference of 
the embryonic disk and are bent in a ventral direction to form the cephalic and 
caudal folds respectively (Figs. 26 and 27). The cephalic fold is first formed, and 
as the proamniotic area (page 47) lying immediately in front of the pericardial 
area (page 47) forms the anterior limit of the circumference of the embryonic 
disk, the forward growth of the head necessarily carries with it the posterior end 
of the pericardial area, so that this area and the buccopharyngeal membrane are 
folded back under the head of the embryo which now encloses a diverticulum of the 
yolk-sac named the fore-gut. The caudal end of the embryo is at first connected 
to the chorion by a band of mesoderm called the body-stalk, but with the formation 
of the caudal fold the body-stalk assumes a ventral position; a diverticulum of the 
yolk-sac extends into the tail fold and is termed the hind-gut. Between the fore-gut 



54 



EMBRYOLOGY 



and the hind-gut there exists for a time a wide opening into the yolk-sac, but the 
latter is gradually reduced to a small pear-shaped sac (sometimes termed the 
umbilical vesicle), and the channel of communication is at the same time narrowed 
and elongated to form a tube called the vitelline duct. 

THE YOLK-SAC. 

The yolk-sac (Figs. 22 and 23) is situated on the ventral aspect of the embryo; 
it is lined by entoderm, outside of which is a layer of mesoderm. It is filled with 
fluid, the vitelline fluid, which possibly may be utilized for the nourislunent of the 
embryo during the earlier stages of its existence. Blood is conveyed to the wall of 
the sac by the primitive aortae, and after circulating through a wide-meshed capil- 
lary plexus, is returned by the vitelline veins to the tubular heart of the embryo. 
This constitutes the vitelline circulation, and by means of it nutritive material is 
absorbed from the yolk-sac and conveyed to the embryo. At the end of the fourth 
week the yolk-sac presents the appearance of a small pear-shaped vesicle (umbilical 
vesicle) opening into the digestive tube by a long narrow tube, the vitelline duct. 
The vesicle can be seen in the after-birth as a small, somewhat oval-shaped body 



Amnion 



Yolk-sac 




Heart 



Hijoid 
Mandibular arch 

Maxillary process 
Eye 



Fore-limb 




Bodv-stalk 
Fig. 22. — Human embrj'o of 2.6 mni. (His.) 



Hind-limb 

Fig. 23. — Human embryo from thirty-one to thirty-four 
days. (His.) 



whose diameter varies from 1 mm. to 5 mm.; it is situated between the amnion 
and the chorion and may lie on or at a varying distance from the placenta. As 
a rule the duct undergoes complete obliteration during the seventh week, but 
in about three per cent, of cases its proximal part persists as a diverticulum 
from the small intestine, Meckel's diverticulum, which is situated about three or 
four feet above the ileocolic junction, and may be attached by a fibrous cord to 
the abdominal wall at the umbilicus. Sometimes a narrowing of the lumen of the 
ileum is seen opposite the site of attachment of the duct. 



DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA. 

The Allantois (Figs. 25 to 28). — The allantois arises as a tubular diverticulum 
of the posterior part of the ^'olk-sac; when the hind-gut is developed the allantois 
is carried backward with it and then opens into the cloaca or terminal part of the 
hind-gut: it grows out into the body-stalk, a mass of mesoderm which lies below 
and around the tail end of the embryo. The diverticulum is lined by entoderm 
and covered by mesoderm, and in the latter are carried the allantoic or umbilical 
vessels. 



DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 55 

In reptiles, birds, and many mammals the allantois becomes expanded into a 
vesicle which projects into the extra-embryonic celom. If its further development 
be traced in the bird, it is seen to project to the right side of the embryo, and, 
gradually expanding, it spreads over its dorsal surface as a flattened sac between 
the amnion and the serosa, and extending in all directions, ultimately surrounds 
the yolk. Its outer wall becomes applied to and fuses with the serosa, which lies 
immediately inside the shell membrane. Blood is carried to the allantoic sac by 



Ainniotic cavity 




Fig. 24. 



Amniotic cavity 
Yolk-sac 

Chorion 



-Diagram showing earliest observed stage 
of human ovum. 




Body-stalk 
Allantois 

• Yolk-sac 



Chorion 



Fio. 25. — Diagram illustrating early formation of 
allantois and differentiation of body-stalk. 



the two allantoic or umbilical arteries, which are continuous with the primitive 
aortse, and after circulating through the allantoic capillaries, is returned to the 
primitive heart by the two umbilical veins. In this way the allantoic circulation, 
which is of the utmost importance in connection with the respiration and nutrition 
of the chick, is established. Oxygen is taken from, and carbonic acid is given up 
to the atmosphere through the egg-shell, while nutritive materials are at the same 
time absorbed by the blood from the yolk. 



Amniotic cavitij 
Embryo 

Body-stalk 



Placental 

villi 




Placental 
villi 



Allantois 



Yolk-sac 



Chorion 



Heart 

Fig. 26 — Diagram showing later stage of allan- 
toic development with commencing constriction 
of the yolk-sac. 




Body-stalk 

Allantois 
Yolk-sac 

Heart 



Fore-gut 
Embryo 
Amniotic cavity 

Fig. 27. — Diagram showing the expansion of amnion 
and delimitation of the umbilicus. 



In man and other primates the nature of the allantois is entirely different from 
that just described. Here it exists merely as a narrow, tubular diverticulum of the 
hind-gut, and never assumes the form of a vesicle outside the embryo. With the 
formation of the amnion the embryo is, in most animals, entirely separated from 
the chorion, and is only again united to it when the allantoic mesoderm spreads 
over and becomes applied to its inner surface. The human embryo, on the other 
hand, as was pointed out by His, is never wholly separated from the chorion, its 



56 



EMBRYOLOGY 



Yolk-sac 

Umbilical cord 

Allantois 
Heart 
Digestive tube 



tail end being from the first connected with the chorion by means of a thick band 
of mesoderm, named the body-stalk (Bauchstiel) ; into this stalk the tube of the 
allantois extends (Fig. 21). 

The Amnion. — The amnion is a membranous sac which surrounds and protects 
the embryo. It is developed in reptiles, birds, and mammals, which are hence 
called "Amniota;" but not in amphibia and fishes, which are consequently termed 
"Anamnia." 

In the human embryo the earliest stages of the formation of the amnion have not 
been observed; in the youngest embryo which has been studied the amnion was 
already present as a closed sac (Figs. 24 and 32), and, as indicated on page 46, 
appears in the inner cell-mass as a cavity. This cavity is roofed in by a single 
stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists 
of the prismatic ectoderm of the embryonic disk — the continuity between the 

roof and floor being established at 
Placental villi the margin of the embryonic disk. 

Outside the amniotic ectoderm is 
a thin layer of mesoderm, which 
is continuous with that of the 
somatopleure and is connected by 
the body-stalk with the meso- 
dermal lining of the chorion. 

When first formed the amnion 
is in contact with the body of the 
embrvo, but about the fourth or 
fifth week fluid (liquor amnii) be- 
gins to accumulate within it. This 
fluid increases in quantity and 
causes the amnion to expand and 
ultimately to adhere to the inner 
surface of the chorion, so that the 
extra-embryonic part of the celom 
is obliterated. The liquor amnii 
increases in quantity up to the 
sixth or seventh month of preg- 
nancy, after which it diminishes 
somewhat; at the end of preg- 
nancy it amounts to about 1 liter. It allows of the free movements of the fetus 
during the later stages of pregnancy, and also protects it by diminishing the risk 
of injury from without. It contains less than 2 per cent, of solids, consisting of 
urea and other extractives, inorganic salts, a small amount of protein, and frequently 
a trace of sugar. That some of the liquor amnii is swallowed by the fetus is proved 
by the fact that epidermal debris and hairs have been found among the contents of 
the fetal alimentary canal. 

In reptiles, birds, and many mammals the amnion is developed in the following 
manner: At the point of constriction where the primitive digestive tube of the 
embryo joins the yolk-sac a reflection or folding upward of the somatopleure takes 
place. This, the amniotic fold (Fig. 29), first makes its appearance at the cephalic 
extremity, and subsequently at the caudal end and sides of the embryo, and grad- 
ually rising more and more, its different parts meet and fuse over the dorsal aspect 
of the embryo, and enclose a cavity, the amniotic cavity. After the fusion of the 
edges of the amniotic fold, the two layers of the fold become completely separated, 
the inner forming the amnion, the outer the false amnion or serosa. The space 
between the amnion and the serosa constitutes the extra-embrj'onic celom, and 
for a time communicates with the embrvonic celom. 




JUmbryo 

Amniotic cavity 

Fia. 28. — Diagram illustrating a later stage in the development 
of the umbilical cord. 



DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 57 

The Umbilical Cord and Body-stalk.— The umbilical cord (Fig. 28) attaches 
the fetus to the placenta; its length at full time, as a rule, is about equal to the 

false amnion or serosa 



vi/ll of 
chono, 





-Tniiscle 
plate 

card .T'ein 

Wolffian body 
and duct 

ccelom 



Fig. 29. — Diagram of a transverse section, showing ttie mode of formation of the amnion in tlie chick. The amniotic 
folds have nearly united ia the middle line. (From Quain's Anatomy.) Ectoderm, blue; mesoderm, red; entoderm 
and notochord, black. 



Umbilical 
cord 

Chorion 



Placenta 




Amnion 



Umbilical 
cord 



Yolk-sac 



Vitelline 
duel 



Fig. 30. — Fetus of about eight weeks, enclosed in the amnion. Magnified a little over two diameters, 
from stereoscopic photographs lent by Prof. A. Thomson. Oxford.) 



(Drawn 



58 



EMBRYOLOGY 



length of the fetus, i. e., about 50 cm., but it may be greatly diminished or increased. 
The rudiment of the umbilical cord is represented by the tissue which connects 
the rapidly growing embryo with the extra-embryonic area of the ovum. Included 
in this tissue are the body-stalk and the vitelline duct— the former containing the 
allantoic diverticulum and the umbilical vessels, the latter forming the communica- 
tion between the digestive tube and the yolk-sac. The body-stalk is the posterior 
segment of the embryonic area, and is attached to the chorion. It consists of a plate 
of mesoderm covered by thickened ectoderm on which a trace of the neural groove 
can be seen, indicating its continuity with the embryo. Running through its 
mesoderm are the two umbilical arteries and the two umbilical veins, together with 
the canal of the allantois — the last being lined by entoderm (Fig. 31). Its dorsal 
surface is covered by the amnion, while its ventral surface is bounded by the extra- 
embrvonic celom, and is in contact with the vitelline duct and volk-sac. With 
the rapid elongation of the embryo and the formation of the tail fold, the bodj' 
stalk comes to lie on the ventral surface of the embryo (Figs. 27 and 28), where 



Splanchnic 
mesoderm 
Entoderm 



Vitelline veins 



Somatic mesoderm 



111 Amniotic cavity 
■ ill — Amnion 

Neural groove 

Neurenteric canal 




Body-stalk 



Fig. 31. — Model of human embrj-o 1.3 mm. long. (After Eternod.) 



its mesoderm blends with that of the yolk-sac and the vitelline duct. The lateral 
leaves of somatopleure then grow round on each side, and, meeting on the ventral 
aspect of the allantois, enclose the vitelline duct and vessels, together with a part 
of the extra-embryonic celom; the latter is ultimately obliterated. The cord is 
covered by a layer of ectoderm which is continuous with that of the amnion, and 
its various constitutents are enveloped by embryonic gelatinous tissue, jelly of 
Wharton. The vitelline vessels and duct, together with the right umbilical vein, 
undergo atrophy and disappear; and thus the cord, at birth, contains a pair of 
umbilical arteries and one (the left) umbilical vein. 

Implantation or Imbedding of the Ovum. — As described (page 44), fertilization 
of the ovum occurs in the lateral or ampullary end of the uterine tube and is 
immediately followed by segmentation. On reaching the cavity of the uterus the 
segmented ovum adheres like a parasite to the uterine mucous membrane, destroys 
the epithelium over the area of contact, and excavates for itself a cavity in the 
mucous membrane in which it becomes imbedded. In the ovum described by 



DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 59 

Bryce and Teacher"^ the point of entrance was visible as a small gap closed by a 
mass of fibrin and leucocytes; in the ovum described by Peters^ the opening was 
covered by a mushroom-shaped mass of fibrin and blood-clot (Fig. 32) , the narrow 
stalk of which plugged the aperture in the mucous membrane. Soon, however, 
all trace of the opening is lost and the ovum is then completely surrounded by the 
uterine mucous membrane. 

The structure actively concerned in the process of excavation is the trophoblast 
of the ovum, which possesses the power of dissolving and absorbing the uterine 
tissues. The trophoblast proliferates rapidly and forms a network of branching 
processes which cover the entire ovum and invade and destroy the maternal 
tissues and open into the maternal bloodvessels, with the result that the spaces 
in the trophoblastic network are filled with maternal blood; these spaces com- 
municate freely with one another and become greatly distended and form the 
intervillous space. 

m.v. /^ ti.Q. tn 




Fig. 32.-Section through ovum imbedded in the uterine decidua. , ^enudiagrammatic (After Peters^) am. 
Amniotic cavity, b.c. Blood-clot. b.s. Body-stalk, ect, Embryomc ectoderm, ent Entoderm mes. Mesoderm. 
m.v. Maternal vessels, tr. Trophoblast. u.e. Uterine epithelmm. u.g. Uterme glands, y.s. \ olk-sac. 

The Decidua.— Before the fertilized ovum reaches the uterus, the mucous 
membrane of the body of the uterus undergoes important changes and is then 
known as the decidua. The thickness and vascularity of the mucous membrane 
are greatly increased; its glands are elongated and open on its free surface by 
funnel-shaped orifices, while their deeper portions are tortuous and dilated into 
irregular spaces. The interglandular tissue is also increased in quantity, and 
is crowded with large round, oval, or polygonal cells, termed decidual cells. These 
changes are well advanced by the second month of pregnancy, when the mucous 
membrane consists of the following strata (Fig. 33): (1) stratum compactum, next 

1 Contribution to the study of the early development and imbedding of the human ovum, 1908. 
« Die Einbettung des menschlichen Eies, 1899. 



60 



EMBRYOLOGY 



Mucous tnembrane 



Muscular fibers 




Stratum compactum 



the free surface; in this the uterine glands are only slightly expanded, and are 
lined by columnar cells; (2) stratum spongiosum, in which the gland tubes are greatly 
dilated and very tortuous, and are ultimately separated from one another by only 
a small amount of interglandular tissue, while their lining cells are flattened or 
cubical; (3) a thin unaltered or boundary layer, next the uterine muscular fibers, 
containing the deepest parts of the uterine glands, which are not dilated, and 

are lined with columnar epithelium; 
it is from this epithelium that the 
epithelial lining of the uterus is re- 
generated after pregnancy. Distinc- 
tive names are applied to different 
portions of the decidua. The part 
which covers in the ovum is named the 
decidua capsularis; the portion which 
intervenes between the ovum and the 
uterine wall is named the decidua 
basalis or decidua placentalis ; it is here 
that the placenta is subsequently 
developed. The part of the decidua 
which lines the remainder of the body 
of the uterus is known as the decidua 
vera or decidua parietalis. 

Coincidently with the growth of 
the embryo, the decidua capsularis is 
thinned and extended (Fig. 34) and 
the space between it and the decidua 
vera is gradually obliterated, so that 
by the third month of pregnancy the 
two are in contact. By the fifth 
month of pregnancy the decidua cap- 
sularis has practically disappeared, 
while during the succeeding months 
the decidua vera also undergoes 
atrophy, owing to the increased press- 
ure. The glands of the stratum com- 
pactum are obliterated, and their 
epithelium is lost. In the stratum 
spongiosum the glands are compressed 
and appear as slit-like fissures, while 
their epithelium undergoes degener- 
ation. In the unaltered or boundary 
layer, however, the glandular epithe- 
lium retains a columnar or cubical 
form. 

The Chorion (Figs. 23 to 28). —The 
chorion consists of two layers : an outer 
formed by the primitive ectoderm or 
trophoblast, and an inner by the soma- 
tic mesoderm; with this latter the amnion is in contact. The trophoblast is made 
up of an internal layer of cubical or prismatic cells, the cytotrophoblast or layer 
of Langhans, and an external layer of richly nucleated protoplasm devoid of cell 
boundaries, the syncytiotrophoblast. It undergoes rapid proliferation and forms 
numerous processes, the chorionic villi, which invade and destroy the uterine 
decidua and at the same time absorb from it nutritive materials for the growth 



Stratum spongiosum 



Unaltered or 
boundary layer 

Muscular fibers 




Fig. 33. — Diagrammatic sections of the uterine mucous 
membrane: A. The non-pregnant uterus. B. The preg- 
nant uterus, showing the thickened mucous membrane 
and the altered condition of the uterine glands. (Kundrat 
and Engelmann.) 



DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA Gl 

of the embryo. The chorionic villi are at first small and non-vascular, and consist 
of trophoblast only, but they increase in size and ramify, while the mesoderm, 
carrying branches of the umbilical vessels, grows into them, and in this way they 
are vascularized. Blood is carried to the villi by the branches of the umbilical 

Placental villi imbedded in the 

^Decidua placentalis 

Uterine tube 



Allantois 



Umbilical cord 
with its con- 
tained vessels 



Non-placental villi im- 
bedded in the decidua 
capsularis 




Cavity of uterus 
~ Yolk-sac 

Cavity of amnion 

Decidua vera 
or parietalis 



Plug of mucus in the 
cervix uteri 



Fig. 34. — Sectional plan of the gravid uterus in the third and fourth month. (Modified from Wagner.) 

arteries, and after circulating through the capillaries of the villi, is returned to 
the embryo by the umbilical veins. Until about the end of the second month 
of pregnancy the villi cover the entire chorion, and are almost uniform in size 
(Fig, 25), but after this they develop unequally. The greater part of the chorion 



Trophoblast 



Mesoderm 




Branches of umbilical vessels 



Fig. 35. — Transverse section of a chorionic villus. 



is in contact with the decidua capsularis (Fig. 34), and over this portion the villi, 
with their contained vessels, undergo atrophy, so that by the fourth month scarcely 
a trace of them is left, and hence this part of the chorion becomes smooth, and is 
named the chorion Iseve; as it takes no share in the formation of the placenta, it 



62 



EMBRYOLOGY 



is also named the non-placental part of the chorion. On the other hand, the villi 
on that part of the chorion which is in contact with the decidua placentalis increase 
greatlv in size and complexity, and hence this part is named the chorion frondosum 
(Fig. 28). 



Uterine vessels 



Uterine glands 




Syncytiotrophoblast 
- — Cytotrophoblasi 



Mesoderm 
Fig. 36. — Primary chorionic villi. 



Intervillous space 
Diagrammatic. (Modified from Bryoe. 



The Placenta. — The placenta connects the fetus to the uterine wall, and is the 
organ by means of which the nutritive, respiratory, and excretory functions of the 
fetus are carried on. It is composed of fetal and maternal portions. 

Fetal Portion. — The fetal portion of the placenta consists of the villi of the 
chorion frondosum; these branch repeatedly, and increase enormously in size. 
These greatly ramified villi are suspended in the intervillous space, and are bathed 



Uterine glands 



Uterine vessels 



Syncytiotrophoblast 

Cytotrophoblasi 

Core of ynesoderm 

with fetal vessels 




Mesoderm Intervillous space 
Fig. 37. — Secondary chorionic villi. Diagrammatic. (Modified from Bryce.) 

in maternal blood, which is conveyed to the space by the uterine arteries and 
carried away by the uterine veins. A branch of an umbilical artery enters each 
villus and ends in a capillary plexus from which the blood is drained by a tributary 
of the umbilical vein. The vessels of the villus are surrounded by a thin layer of 
mesoderm consisting of gelatinous connective tissue, which is covered by two 



DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 63 

strata of ectodermal cells derived from the trophoblast: the deeper stratum, 
next the mesodermic tissue, represents the cytotrophoblast or layer of Langhans; 
the superficial, in contact with the maternal blood, the syncytiotrophoblast (Figs. 
36 and 37). After the fifth month the two strata of cells are replaced by a 
single layer of somewhat flattened cells. 

Maternal Portion. — The maternal portion of the placenta is formed by the 
decidua placentalis containing the intervillous space. As already explained, this 
space is produced by the enlargement and intercommunication of the spaces in 
the trophoblastic network. The changes involve the disappearance of the greater 
portion of the stratum compactum, but the deeper part of this layer persists and 
is condensed to form what is known as the basal plate. Between this plate and 
the uterine muscular fibres are the stratum spongiosum and the boundary layer ; 



Wall of uterus 




Umbilical cord 



Cervix uteri 



Fig. 38. — Fetus in utero, between fifth and sixth months. 



through these and the basal plate the uterine arteries and veins pass to and from 
the intervillous space. The endothelial lining of the uterine vessels ceases at the 
point where they terminate in the intervillous space which is lined by the syncytio- 
trophoblast. Portions of the stratum compactum persist and are condensed to 
form a series of septa, which extend from the basal plate through the thickness 
of the placenta and subdivide it into the lobules or cotyledons seen on the uterine 
surface of the detached placenta. 

The fetal and maternal blood currents traverse the placenta, the former passing 
through the bloodvessels of the placental \'illi and the latter through the inter- 
villous space (Fig. 39) . The two currents do not intermingle, being separated from 
each other by the delicate walls of the villi. Nevertheless, the fetal blood is able 
to absorb, through the walls of the villi, oxygen and nutritive materials from the 



64 



EMBRYOLOGY 



maternal blood, and give up to the latter its waste products. The blood, so purified, 
is carried back to the fetus by the umbilical vein. It will thus be seen that the 
placenta not only establishes a mechanical connection between the mother and the 
fetus, but subserves for the latter the purposes of nutrition, respiration, and ex- 
cretion. In favor of the view that the placenta possesses certain selective powers 
may be mentioned the fact that glucose is more plentiful in the maternal than in 
the fetal blood. It is interesting to note also that the proportion of iron, ancj of 
lime and potash, in the fetus is increased during the last months of pregnancy. 
Further, there is evidence that the maternal leucocytes may migrate into the fetal 
blood, since leucocytes are much more numerous in the blood of the umbilical vein 
than in that of the umbilical arteries. 

The placenta is usually attached near the fundus uteri, and more frequently on 
the posterior than on the anterior wall of the uterus. It may, however, occupy 
a lower position and, in rare cases, its site is close to the orificium internum uteri, 
which it may occlude, thus giving rise to the condition known as placenta previa. 



Stratum spongiosum 
Limiting or boundary layer 
Maternal vessels 



Placental septum 



Villus 




Chorion 
Marginal sinus 

Fig. 39. — Scheme of placental circulation. 

Separation of the Placenta. — -After the child is born, the placenta and membranes 
are expelled from the uterus as the after-birth. The separation of the placenta from 
the uterine wall takes place through the stratum spongiosum, and necessarily 
causes rupture of the uterine vessels. The orifices of the torn vessels are, how^ever, 
closed by the firm contraction of the uterine muscular fibers, and thus postpartum 
hemorrhage is controlled. The epithelial lining of the uterus is regenerated by the 
proliferation and extension of the epithelium which lines the persistent portions 
of the uterine glands in the unaltered layer of the decidua. 

The expelled placenta appears as a discoid mass which weighs about 450 gm. 
and has a diameter of from 15 to 20 cm. Its average thickness is about 3 cm., 
but this diminishes rapidly toward the circumference of the disk, which is continu- 
ous with the membranes. Its uterine surface is divided by a series of fissures into 
lobules or cotyledons, the fissures containing the remains of the septa which extended 
between the maternal and fetal portions. Most of these septa end in irregular 
or pointed processes; others, especially those near the edge of the placenta, pass 



THE BRANCHIAL REGION 



65 



through its thickness and are attached to the chorion. In the early months tliese 
septa convey branches of the uterine arteries which open into the intervillous 
space on the surfaces of the septa. The fetal surface of the placenta is smooth, 
being closely invested by the amnion. Seen through the latter, the chorion 
presents a mottled appearance, consisting of gray, purple, or yellowish areas. 
The umbilical cord is usually attached near the center of the placenta, but 
may be inserted anywhere between the center and the margin; in some cases it 
is inserted into the membranes, i. e., the velamentous insertion. From the attach- 
ment of the cord the larger branches of the umbilical vessels radiate under the 
amnion, the veins being deeper and larger than the arteries. The remains of 
the vitelline duct and yolk-sac may be sometimes observed beneath the amnion, 
close to the cord, the former as an attenuated thread, the latter as a minute sac. 
On section, the placenta presents a soft, spongy appearance, caused by the 
greatly branched villi; surrounding them is a varying amount of maternalblood 
giving the dark red color to the placenta. Many of the larger villi extend from 
the chorionic to the decidual surface, while others are attached to the septa which 
separate the cotyledons; but the great majority of the villi hang free in the inter- 
villous space. 



Mid-brain 



Fore-brain 
Stomodeum 



Mandibular arch 

irt %. 



Hea 




Himl-hrain 

Auditory vesicle 



Visceral 
arches 



Amnion (cut) 




Olfactory pit / \ w, 

Maxillary process /) 

Mandibular arch 

Hyoid arch 

Third arch 



Fig. 40.- 



Body-stalk 



-Embryo between eighteen and twenty-one 
days. (His.) 



Fig. 41. — Head end of human embryo, about the end 
of the fourth week. (From model by Peter.) 



THE BRANCHIAL REGION. 

The Branchial or Visceral Arches and Pharyngeal Pouches. — In the lateral walls 
of the anterior part of the fore-gut five pharyngeal i)ouches appear (Fig. 42) ; each 
of the upper four pouches is prolonged into a dorsal and a ventral diverticulum. 
Over these pouches corresponding indentations of the ectoderm occur, forming what 
are known as the branchial or outer pharyngeal grooves. The intervening mesoderm 
is pressed aside and the ectoderm comes for a time into contact with the ento- 
dermal lining of the fore-gut, and the two layers unite along the floors of the 
grooves to form thin closing membranes between the fore-gut and the exterior. 
Later the mesoderm again penetrates between the entoderm and the ectoderm. 
In gill-bearing animals the closing membranes disappear, and the grooves become 
5 



66 



EMBRYOLOGY 



Lateral tongue Thyroid 
elevations diverticvlum 



complete clefts, the gill-clefts, opening from the pharynx on to the exterior; perfo- 
ration, however, does not occur in birds or mammals. The grooves separate a 
series of rounded bars or arches, the branchial or visceral arches, in which thickening 
of the mesoderm takes place (Figs. 40 and 41). The dorsal ends of these arches 
are attached to the sides of the head, while the ventral extremities ultimately 
meet in the middle line of the neck. In all, six arches make their appearance, 
but of these only the first four are visible externally. The first arch is named the 

mandibular, and the second the hyoid; the 
others have no distinctive names. In each 
arch a cartilaginous bar, consisting of right 
and left halves, is developed, and with each 
of these there is one of the primitive aortic 
arches. 

The mandibular arch lies between the first 
branchial groove and the stomodeum; from it 
are developed the lower lip, the mandible, 
the muscles of mastication, and the anterior 
part of the tongue. Its cartilaginous bar is 
formed by what are known as Meckel's carti- 
lages (right and left) (Fig. 43) ; above this the 
incus is developed. The dorsal end of each 
cartilage is connected with the ear-capsule 
and is ossified to form the malleus; the ventral ends meet each other in the region 
of the symphysis menti, and are usually regarded as undergoing ossification to form 
that portion of the mandible which contains the incisor teeth. The intervening 
part of the cartilage disappears; the portion immediately adjacent to the malleus is 
replaced by fibrous membrane, which constitutes the spheno-mandibular ligament, 




Entrance to 
larynx 



Fig. 42. — Floor of pharvux of embryo shown in 
Fig. 40. 



Malleus 



Incus 




Tympanic ring 
■ Jlandible 



■ ~- Meckel's cartilage 



Hyoid hone 



Fig. 43. — Head and neck of a human embryo eighteen weeks old, with Meckel's cartilage and hyoid bar exposed. 

(After KoUiker.) 



while from the connective tissue covering the remainder of the cartilage the greater 
part of the mandible is ossified. From the dorsal ends of the mandibular arch a 
triangular process, the maxillary process, grows forward on either side and forms 
the cheek and lateral part of the upper lip. The second or hyoid arch assists in 
forming the side and front of the neck. From its cartilage are developed the styloid 
process, stylohyoid ligament, and lesser cornu of the hyoid bone. The stages prob- 



THE BRANCHIAL REGION 



G7 



ably arises in the upper part of this arch. Tlie cartilage of the third arch gives origin 
to the greater cornu of the hyoid bone. The ventral ends of the second and third 
arches unite with those of the opposite side, and form a transverse band, from 
which the body of the hyoid bone and the posterior part of the tongue are devel- 
oped. The ventral portions of the cartilages of the fourth and fifth arches unite 
to form the thyroid cartilage; from the cartilages of the sixth arch the cricoid 
and arytenoid cartilages and the cartilages of the trachea are developed. The 
mandibular and hyoid arches grow more rapidly than those behind them, with 
the result that the latter become, to a certain extent, telescoped within the 
former, and a deep depression, the sinus cervicalis, is formed on either side of 
the neck. This sinus is bounded in front by the hyoid arch, and behind by the 
thoracic wall; it is ultimately obliterated by the fusion of its walls. 

From the first branchial groove the concha auricuke and external acoustic 
meatus are developed, while around the groove there appear, on the mandibular 
and hyoid arches, a number of swellings from which the auricula or pinna is formed. 
The first pharyngeal pouch is prolonged dorsally to form the auditory tube and the 
tympanic cavity; the closing membrane between the mandibular and hyoid arches 

Memhranoiis capsule over cerebral hemisphere 



Fronto-nasal process 



Stomodeiun 




Lateral nasal process 

Eije 

Globular process 
Maxillary process 

Mandibular arch 
Hyomandibular deft 



Fig. 44. — Under surface of the head of a human embryo about twenty-nine daj's old. (After His.) ' 

is invaded by mesoderm, and forms the tympanic membrane. No traces of the 
second, third, and fourth branchial grooves persist. The inner part of the second 
pharyngeal pouch is named the sinus tonsillaris ; in it the tonsil is developed, above 
which a trace of the sinus persists as the supratonsillar fossa. The fossa of Rosen- 
miiller or lateral recess of the pharynx is by some regarded as a persistent part of 
the second pharyngeal pouch, but it is probably developed as a secondary forma- 
tion. From the third pharyngeal pouch the thymus arises as an entodermal diver- 
ticulum on either side, and from the fourth pouches small diverticula project and 
become incorporated with the thymus, but in man these diverticula probably 
never form true thymus tissue. The parathyroids also arise as diverticula from 
the third and fourth pouches. From the fifth pouches the ultimobranchial bodies 
originate and are enveloped by the lateral prolongations of the median thyroid 
rudiment; they do not, however, form true thyroid tissue, nor are any traces 
of them found in the human adult. 

The Nose and Face. — During the third week two areas of thickened ectoderm, the 
olfactory areas, appear immediately under the fore-brain in the anterior wall of the 
stomodeum, one on either side of a region termed the fronto-nasal process (Fig. 44). 
By the upgrowth of the surrounding parts these areas are converted into pits. 



68 



EMBRYOLOGY 



the olfactory pits, which indent the fronto-nasal process and divide it into a 
medial and two lateral nasal processes (Fig. 45). The rounded lateral angles of 
the medial process constitute the globular processes of His. The olfactory pits form 




Future apex of nose 

Medial nasal process 

Olfactory pit 
Lateral na.sal process 
Glchular process 
Maxillary process 
Stoinodeum 

Mandibular arch 




Future apex of nose 

Medial nasal process 

Olfactory pit 

Lateral nasal process 

Globular process 
Maxillary process 

Hoof of pharynx 
Hypophyseal diverticulum 

Dorsal uxill of pharynx 



Fig. 45. — Head end of human embryo of about thirty 
to thirty-one days. (From model by Peters.) 



Fig. 46. — Same embryo as shown in Fig. 45, with front 
wall of pharynx removed. 



the rudiments of the nasal cavities, and from their ectodermal lining the epithe- 
lium of the nasal cavities, with the exception of that of the inferior meatuses, is 
<leri\ ed. The globular processes are prolonged backward as plates, termed the nasal 
laminae: these laminae are at first some distance apart, but, gradually approach- 





Lateral nasal pro- 
cess 
Globular processes 



Fig. 47. — Head of a human embryo of 
about eight weeks, in which the nose and 
mouth are formed. (His.) 



Fig. 48. — Diagram showing the regions of the adult face and neck 
related to the fronto-nasal process and the branchial arches. 



ing, they ultimately fuse and form the nasal septum; the processes themselves 
meet in the middle line, and form the premaxillae and the philtrum or central 
part of the upper lip (Fig. 48). The depressed part of the medial nasal process 



THE BRANCHIAL REGION 



69 



between the globular processes forms the lower part of the nasal septum or 
columella; while above this is seen a prominent angle, which becomes the future 
apex (Figs. 45, 46), and still higher a flat area, the future bridge, of the nose. 
The lateral nasal processes form the alae of the nose. 

Continuous with the dorsal end of the mandibular arch, and growing forward 
from its cephalic border, is a triangular process, the maxillary process, the ventral 
extremity of which is separated from the mandibular arch by a > shaped notch 



Nares 



Primitive 

palate 




Nasal 
cavity 



Bucconasal 
niembranes 

Fig. 49. — Primitive palate of a human embryo of thirty-seven to thirty-eight days. (From model by Peters.) 
On the left side the lateral wall of the nasal cavity has been removed. 

(Fig. 44). The maxillary process forms the lateral wall and floor of the orbit, 
and in it are ossified the zygomatic bone and the greater part of the maxilla; it 
meets with the lateral nasal process, from which, however, it is separated for a 
time by a groove, the naso-optic furrow, that extends from the furrow encircling 
the eyeball to the olfactory pit. The maxillary processes ultimately fuse with the 
lateral nasal and globular processes, and form the lateral parts of the upper lip 



Globtdar process 

\ 
Palatine process of 
globular proces6 

Palatine part of 
maxillary process 

Maxillary process 



Mouth of olfactory 
pit, or naris 




Pharynx 



Fig. 50 — The roof of the mouth of a human embryo, aged about two and a half months, showing the mode of 

formation of the palate. (His.) 



and the posterior boundaries of the nares (Figs. 47, 48). From the third to 
the fifth month the nares are filled by masses of epithelium, on the breaking down 
and disappearance of which the permanent openings are produced. The maxillary 
process also gives rise to the lower portion of the lateral wall of the nasal cavity. 
The roof of the nose and the remaining parts of the lateral wall, viz., the ethmoidal 
labyrinth, the inferior nasal concha, the lateral cartilage, and the lateral crus of 
the alar cartilage, are developed in the lateral nasal process. By the fusion of the 



70 



EMBRYOLOGY 



maxillary and nasal processes in the roof of the stomodeum the primitive palate 
(Fig. 49) is formed, and the olfactory pits extend backward above it. The pos- 
terior end of each pit is closed by an epithelial membrane, the bucco-nasal membrane, 
formed by the apposition of the nasal and stomodeal epithelium. By the rupture 
of these membranes the primitive choanae or openings between the olfactory pits 
and the stomodeum are established. The jfloor of the nasal cavity is completed 
by the development of a pair of shelf-like palatine processes which extend medial- 
ward from the maxillary processes (Figs. 50 and 51); these coalesce with each 
other in the middle line, and constitute the entire palate, except a small part in 
front which is formed by the premaxillary bones. Two apertures persist for a time 
between the palatine processes and the premaxillse and represent the permanent 
channels which in the lower animals connect the nose and mouth. The union of 
the parts which form the palate commences in front, the premaxillary and palatine 
processes joining in the eighth week, while the region of the future hard palate 




Lateral 'part of^ 
nasal capsule 



Inferior meatus 

Vomeronasal 
cartilage 



Palatine process- 






Cartilage of 
nasal septum 



omeronasal 
organ of Jacobson 






75-\;'v-.5;;)?'^.v;:. 




fy( -M^^-'- 



• Inferior meatus 



m 




Cavity of mouth 



Fig. 51. — Frontal section of nasal cavities of a human embryo 28 mm. long. (Kollmann.) 

is completed by the ninth, and that of the soft palate by the eleventh week. By 
the completion of the palate the permanent choanae are formed and are situated a 
considerable distance behind the primiti\"e choanse. The deformity known as 
cleft palate results from a non-union of the palatine processes, and that of hare- 
lip through a non-union of the maxillary and globular processes (see page 199). 
The nasal cavity becomes divided by a vertical septum, which extends downward 
and backward from the medial nasal process and nasal laminae, and unites below 
with the palatine processes. Into this septum a plate of cartilage extends from 
the under aspect of the ethmoid plate of the chodrocranium. The anterior part 
of this cartilaginous plate persists as the septal cartilage of the nose and the medial 
crus of the alar cartilage, but the posterior and upper parts are replaced by the 
vomer and perpendicular plate of the ethmoid. On either side of the nasal septum, 
at its lower and anterior part, the ectoderm is invaginated to form a blind pouch 
or diverticulum, which extends backward and upward into the nasal septum and 
is supported by a curved plate of cartilage. , These pouches form the rudiments of 



THE BRANCHIAL REGION 



71 



the vomero-nasal organs of Jacobson, which open below, close to the junction 
of the premaxillary and maxillary bones. 

The Limbs. — The limbs begin to make their appearance in the third week as 
small elevations or buds at the side of the trunk (Fig. 52). Prolongations from 
the muscle- and cutis-plates of several primitive segments extend into each bud, 
and carry with them the anterior divisions of the corresponding spinal nerves. 
The nerves supplying the limbs indicate the number of primitive segments which 
contribute to their formation — the upper limb being derived from seven, viz., 
fourth cervical to second thoracic inclusive, and the lower limb from ten, viz., 
twelfth thoracic to fourth sacral inclusive. The axial part of the mesoderm of 
the limb-bud becomes condensed and converted into its cartilaginous skeleton, 
and by the ossification of this the bones of the limbs are formed. By the sixth 
week the three chief divisions of the limbs are marked off by furrows — the upper 
into arm, forearm, and hand; the lower into thigh, leg, and foot (Fig. 53). The 
limbs are at first directed backward nearly parallel to the long axis of the trunk, 



Heart 



Mandibu 
Maxillary piocess 




Auricula 



- Fure-limb 



Hind-limb 



Fig. 52. — Human embryo from thirty-one to thirty- 
four days. (His.) 



Umbilical cord 

Fig. 53. — Embryo of about six weeks. (His. 



and each presents two surfaces and two borders. Of the surfaces, one — the future 
flexor surface of the limb — is directed ventrally; the other, the extensor surface, 
dorsally; one border, the preaxial, looks forward toward the cephalic end of the 
embryo, and the other, the postaxial, backward toward the caudal end. The lateral 
epicondyle of the humerus, the radius, and the thumb lie along the preaxial border 
of the upper limb; and the medial epicondyle of the femur, the tibia, and the great 
toe along the corresponding border of the lower limb. The preaxial part is derived 
from the anterior segments, the postaxial from the posterior segments of the limb- 
bud; and this explains, to a large extent, the innervation of the adult limb, the 
nerves of the more anterior segments being distributed along the preaxial (radial 
or tibial), and those of the more posterior along the postaxial (ulnar or fibular) 
border of the limb. The limbs next undergo a rotation or torsion through an angle 
of 90° around their long axes the rotation being effected almost entirely at the 
limb girdles. In the upper limb the rotation is outward and forward; in the lower 
limb, inward and backward. As a consequence of this rotation the preaxial (radial) 



72 



EMBRYOLOGY 



border of the fore-limb is directed lateralward, and the preaxial (tibial) border 
of the hind-limb is directed mediahvard; thus the flexor surface of the fore-limb 
is turned forward, and that of the hind-limb backward. 

DEVELOPMENT OF THE BODY CAVITIES. 

In the human embryo described by Peters the mesoderm outside the embryonic 
^isk is split into two layers enclosing an extra-embryonic coelom; there is no trace 
of an intra-embryonic coelom. At a later stage four cavities are formed within the 
embryo, viz., one on either side within the mesoderm of the pericardial area, and 
one in either lateral mass of the general mesoderm. All these are at first independent 
of each other and of the extra-embryonic celom, but later they become continuous. 
The two cavities in the general mesoderm unite on the ventral aspect of the gut 
and form the pleuro-peritoneal cavity, which becomes continuous with the remains 
of the extra-embryonic celom around the umbilicus; the two, cavities in the peri- 
cardial area rapidly join to form a single pericardial cavity, and this from two lateral 
diverticula extend caudalward to open into the pleuro-peritoneal cavity (Fig. 54). 



Mesentery 



Pleural cav>ty\^ 



iMtvg. 



Phuro- pericardial.— 
opening 



Pericardium 




Mesoderm 

surrounding 

duct ofCuvier 



■'] -Dorsal mesocardiv/m 
'~\"~Heart 



Fig. 54. — Figure obtained by combining several successive sections of a human embryo of about the fourth week 
(From KoUmann.) The upper arrow is in the pleuroperitoneal opening, the lower in the pleuropericardial. 



Between the two latter diverticula is a mass of mesoderm containing the ducts 
of Cuvier, and this is continuous ventrally with the mesoderm in which the umbili- 
cal veins are passing to the sinus venosus. A septum of mesoderm thus extends 
across the body of the embryo. It is attached in front to the body-wall between 
the pericardium and umbilicus; behind to the body-wall at the level of the second 
cervical segment; laterally it is deficient where the pericardial and pleuro-peri- 
toneal cavities communicate, while it is perforated in the middle line by the fore- 
gut. This partition is termed the septum transversum, and is at first a bulky plate 
of tissue. As development proceeds the dorsal end of the septum is carried grad- 
ually caudalward, and when it reaches the fifth cervical segment muscular tissue 
with the phrenic nerve grows into it. It continues to recede, however, until it 
reaches the position of the adult diaphragm on the bodies of the upper lumbar 
vertebrae. The liver buds grow into the septum transversum and undergo 
development there. 

The lung buds meantime have grown out from the fore-gut, and project laterally 
into the forepart of the pleuro-peritoneal cavity; the developing stomach and liver 
are imbedded in the septum transversum; caudal to this the intestines project into 
the back part of the pleuro-peritoneal cavity (Fig. 55). Owing to the descent of 



DEVELOPMENT OF THE BODY CAVITIES 



73 



the dorsal end of the septum transversum the lung buds come to lie above tlie 
septum and thus pleural and peritoneal portions of the pleuro-peritoneal cavity 
(still, however, in free communication with one another) may be recognized; the 
pericardial cavity opens into the pleural part. 



Left due of Cuvier Esofliagus Bight duct of Cuvier 



Me.ioderm 

surrounding duct 

Pleura- pericardial 

opening 
Rid'je growing across 

opening 



Omental bursa — r 



Stomach i 




—Dorsal mesentery 



Peritoneal recess 



Fia. 55. — Upper part of celom of human embryo of 6.8 mm., seen from behind. (From model by Piper.) 



The ultimate separation of the permanent cavities from one another is effected 
by the growth of a ridge of tissue on either side from the mesoderm surrounding 



Msopliagus 




Aorta 

Pleural cavity 
Lung 

Inferior vena cava 



YBody wall 



Pericardium 



Fia. 56. — Diagram of transverse section through rabbit embryo, (.\fter Keith.) 



the duct of Cuvier (Figs. 54, 55). The front part of this ridge grows across and 
obliterates the pleuro-pericardial opening; the hinder part grows across the pleuro- 
peritoneal opening. 

With the continued growth of the lungs the pleural cavities are pushed forward 



74 



EMBRYOLOGY 



in the body-wall toward the ventral median line, thus separating the pericardium 
from the lateral thoracic walls (Fig. 53) . The further development of the peritoneal 
cavity has been described with the development of the digestive tube (page 168 
et seq.). 



Stemn-cnstal 2>art of 
JJiaphra(/ina 
Central tendon of Diaphragm a 

Inferior vena cava 



Spleen 

Colon 

Suprarenal gland 

Eleventh rib 



Twelfth rib 




(Esophagus 

Vertebral part of Diaphragma 

Posterior tnediastinal cavity 

Aorta 



Spino-costal hiatus 



Left pleura 



Right pleura 



Fig. 57. — The thoracic aspect of the diaphragm of a newly born child in which the communication between the 
peritoneum and pleura has not been closed on the left side; the position of the opening is marked on the right side by 
the spinocostal hiatus. (After Keith.) 



THE FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH. 

First Week. — During this period the ovum is in the uterine tube. Having been fertiHzed in 
the upper part of the tube, it slowly passes down, undergoing segmentation, and reaches the 
uterus. Peters' described a specimen, the age of which he reckoned as from three to four days. 
It was imbedded in the decidua on the posterior wall of the uterus and enveloped by a decidua 
capsularis, the central part of which, however, consisted merely of a layer of fibrin. The ovum 
was in the form of a sac, the outer wall of which consisted of a layer of trophoblast; inside thia 



Arrmion 



Heart 




Body-stalk 



Chorion 
Fig. 58. — Human embryo about fifteen day-s old. 



(His.) 



was a thin layer of mesoderm composed of round, oval, and spindle-shaped cells. Numerous 
villous processes — some consisting of trophoblast only, others possessing a core of mesoderm — 
projected from the surface of the ovum into the surrounding decidua. Inside this sac the rudi- 
ment of the embryo was found in the form of a patch of ectoderm, covered by a small but com- 



1 Die Einbettung des menschlichen Eies, 1899. 



FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 75 

pletely closed amnion. It possessed a minute yolk-sac and was surrounded by mesoderm, which 
was connected by a band to that lining the trophoblast (Fig. 32).^ 

Second Week. — By the end of this week the ovum has increased considerably in size, and the 
majority of its vilU are vascularized. The embryo has assumed a definite form, and its cephahc 
and caudal extremities are easily distinguished. The neural folds are partly united. The embryo 



Mid-brain 



Fore-hram 



Stomodeum 



Mandibular arch 
Heart 




Hind-brain 

Auditory vesicle 

^ Visceral 

arches 



Amnion (cut) 



Body-stalk 
Fig. 59. — Human embryo between eighteen and twenty-one days old. (His. 



is more completely separated from the yolk-sac, and the paraxial mesoderm is being divided into 
the primitive segments (Fig. 58). 

Third Week. — By the end of the third week the embryo is strongly curved, and the primitive 
segments number about thirty. The primary divisions of the brain are visible, and the optic 



Fore-htnb 



Hyoid arch 

. Mandibular arch 
Maxillary process 

Eye 
Olfactory pit 




Chorion ^ CL 



Fig. 60.- 



•r, .J , Hind-hmh 
-Human embryo, twenty-seven to thirty days old. (His.) 



and auditory vesicles are formed. Four branchial grooves are present: the stomodeum is well- 
marked, and the bucco-pharyngeal membrane has disappeared. The rudiments of the hmbs 
are seen as short buds, and the Wolffian bodies are visible (Fig. 59). 

1 Bryce and Teacher (Early Deielopment and Imbedding of (he Human Ovum, 190S) have described an ovum which 
they regard as thirteen to fourteen days old. In it the two vesicles, the amnion and yolk-sac, were present, but there 
was no trace of a layer of embryonic ectoderm. They are of opinion that the age of Peters ovum has been understated, 
and estimate it as between thirteen and one-half and fourteen and one-half days. 



76 



EMBRYOLOGY 



Fourth Week. — The embryo is markedly curved on itself, and when viewed in profile is almost 
circular in outhne. The cerebral hemispheres appear as hollow buds, and the elevations which 
form the rudiments of the auricula are visible. The limbs now appear as oval flattened projec- 
tions (Fig. 60). 

Heart 



Hyoid arch 
Mandibular arch 

Maxillary process 
Eye 



Fore-limb 




Hind-limh 
Fig. 01. — Human embryo, thirty-one to thirty-four days old. (His.) 



Fifth Week. — The embryo is less curved and the head is relatively of large size. Differentiation 
of the limbs into their segments occurs. The nose forms a short, flattened projection. The cloacal 
tubercle is evident (Fig. Gl). 




Auricula 



Fore-limb 



Mind-limb 



Umbilical cord 



Fig. 62. — Human embryo of about six weeks. 
(His.) 




Fig. 63. — Human embryo about eight and a half 
weeks old. (His.) 



Sixth Week.— The curvature of the embryo is further diminished. The branchial grooves— 
except the first — have disappeared, and the rudiments of the fingers and toes can be recognized 
(Fig. 62). 

Seventh and Eighth Weeks. — The flexure of the head is gradually reduced and the neck is 
somewhat lengthened. The upper lip is completed and the nose is more prominent. The nostrils 



FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 77 

are directed forward and the palate is not completely developed. The eyelids are present in the 
shape of folds above and below the eye, and the different parts of the auricula are distinguish- 
able. • By the end of the second month the fetus measures from 28 to 30 mm. in length (Fig. 63). 

Third Month.— The head is extended and the neck is lengthened. The eyelids meet and fuse, 
remaining closed until the end of the sixth month. The limbs are well-developed and nails appear 
on the digits. The external generative organs are so far differentiated that it is possible to dis- 
tinguish the sex. By the end of this month the length of the fetus is about 7 cm., but if the legs 
be included it is from 9 to 10 cm. 

Fourth Month. — The loop of gut which projected into the umbiUcal cord is withdrawn withm 
the fetus. The hairs begin to make their appearance. There is a general increase in size so that 
by the end of the fourth month the fetus is from 12 to 13 cm. in length, but if the legs be included 
it is from 16 to 20 cm. 

Fifth Month. — It is during this month that the first movements of the fetus are usually ob- 
served The eruption of hair on the head commences, and the vernix caseosa begins to be deposited. 
By the end of this month the total length of the fetus, including the legs, is from 25 to 27 cm 

Sixth Month. — The body is covered by fine hairs (lanugo) and the deposit of vernix caseosa 
is considerable. The papillae of the skin are developed and the free border of the nail projects 
from the corium of the dermis. Measured from vertex to heels, the total length of the fetus 
at the end of this month is from 30 to 32 cm. 

Seventh Month. — ^The pupillary membrane atrophies and the eyehds are open. The testis 
descends with the vaginal sac of the peritoneum. From vertex to heels the total length at the 
end of the seventh month is from 35 to 36 cm. The weight is a little over three pounds. 

Eighth Month. — The skin assumes a pink color and is now entirely coated with vernix caseosa, 
and the lanugo begins to disappear. Subcutaneous fat has been developed to a considerable 
extent, and the fetus presents a plump appearance. The total length, i. e., from head to heels, 
at the end of the eighth month is about 40 cm., and the weight varies between four and one-half 
and five and one-half pounds. 

Ninth Month. — The lanugo has largely disappeared from the trunk. The umbihcus is almost 
in the middle of the body and the testes are in the scrotum. At full time the fetus weighs from 
six and one-half to eight pounds, and measures from head to heels about 50 cm. 

BIBLIOGRAPHY. 

Broman: Normal e und abnorme Entwicklung des Menschen, 1911. 

Bryce, Teacher and Kerr: Contributions to the Study of the Early Development and 
Imbedding of the Human Ovum, 1908. 

Hertwig, O.: Handbuch der Vergleichenden und Experimentellen Entwicklungslehre der 
Wirbeltiere, 1906. 

His, W. : Anatomic menschlicher Embryonen, 1883-1885. 

Hochstetter, F.: Bilder der iiusseren Koperform einiger menschlicher Embryonen aus den 
beiden ersten Monaten der Entwicklung, 1907. 

Keibel and Elze: Normentafel zur Entwicklungsgescliichte des Menschen, 1908. 

Keibel and Mall: Manual of Human Embryology, 1910-1912. 



KOLLMANN, J 
KOLLMANN, J. 



Handatlas der Entwickhmgsgeschichte des Menschen, 1907. 
Lehrbuch der Entwicklungsgescliichte des Menschen, 1898. 
Mall: Contribution to the Study of the Pathology of the Human Embryo, Jour, of Morph., 
1908. See also contributions to Embryology of the Carnegie Institution of Washington. 
Mall: Development of the Human Ccelom, Jour, of Morph., 1897. 

Peters, H.: Ueber die Einbettung des menschl ichen Eies und das friiheste bisher bekannte 
menschliche Placentationsstadium, 1899. 



OSTEOLOGY. 



rpHE general framework of the body is built up mainly of a series of bones, 
-L supplemented, however, in certain regions by pieces of cartilage; the bony 
part of the framework constitutes the skeleton. 

In the skeleton of the adult there are 206 distinct bones, as follows:— 

' Vertebral column . . . . .26 

Axial I Skull 22 

Skeleton | Hyoid bone ... . . . .1 

, Ribs and sternum . . . . .25 

— 74 
Appendicular / Upper extremities 64 

Skeleton \ Lower extremities . . . . .62 

— 126 
Auditory ossicles ........ 6 

Total ..... 206 

The patellae are included in this enumeration, but the smaller sesamoid bones 
are not reckoned. 

Bones are divisible into four classes: Long, Short, Flat, and Irregular. 

Long Bones. — The long bones are found in the limbs, and each consists of a body 
or shaft and two extremities. The body, or diaphysis is cylindrical, with a central 
cavity termed the medullary canal; the wall consists of dense, compact tissue 
of considerable thickness in the middle part of the body, but becoming thinner 
toward the extremities; within the medullary canal is some cancellous tissue, 
scanty in the middle of the body but greater in amount toward the ends. The 
extremities are generally expanded, for the purposes of articulation and to afford 
broad surfaces for muscular attachment. They are usually developed from sep- 
arate centers of ossification termed epiphyses, and consist of cancellous tissue 
surrounded by thin compact bone. The medullary canal and the spaces in the 
cancellous tissue are filled with marrow.- The long bones are not straight, but 
curved, the curve generally taking place in two planes, thus afi'ording greater 
strength to the bone. The bones belonging to this class are: the clavicle, humerus, 
radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, and phalanges. 

Short Bones. — Where a part of the skeleton is intended for strength and com- 
pactness combined with limited movement, it is constructed of a number of short 
bones, as in the carpus and tarsus. These consist of cancellous tissue covered 
by a thin crust of compact substance. The patellae, together with the other 
sesamoid bones, are by some regarded as short bones. 

Flat Bones. — Where the principal requirement is either extensive protection or 
the provision of broad surfaces for muscular attachment, the bones are expanded 
into broad, flat plates, as in the skull and the scapula. These bones are composed 
of two thin layers of compact tissue enclosing between them a variable quantity 
of cancellous tissue. In the cranial bones, the layers of compact tissue are famili- 
arly known as the tables of the skull; the outer one is thick and tough; the inner 
is thin, dense, and brittle, and hence is termed the vitreous table. The intervening 

(79) 



80 OSTEOLOGY 

cancellous tissue is called the diploe, and this, in certain regions of the skull, 
becomes absorbed so as to leave spaces filled with air (air-sinuses) between 
the two tables. The flat bones are: the occipital, parietal, frontal, nasal, lacrimal, 
vomer, scapula, os coxae (hip hone), sternum, ribs, and, according to some, the 
patella. 

Irregular Bones. — The irregular bones are such as, from their peculiar form, 
cannot be grouped under the preceding heads. They consist of cancellous tissue 
enclosed within a thin layer of compact bone. The irregular bones are: the 
vertebrae, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, 
palatine, inferior nasal concha, and hyoid. 

Surfaces of Bones. — If the surface of a bone be examined, certain eminences 
and depressions are seen. These eminences and depressions are of two kinds: 
articular and non-articular. Well-marked examples of articular eminences are 
found in the heads of the humerus and femur; and of articular depressions in the 
glenoid cavity of the scapula, and the acetabulum of the hip bone. Non-articular 
eminences are designated according to their form. Thus, a broad, rough, uneven 
elevation is called a tuberosity, protuberance, or process, a small, rough prominence, 
a tubercle ; a sharp, slender pointed eminence, a spine ; a narrow, rough elevation, 
running some way along the surface, a ridge, crest, or line. Non-articular depres- 
sions are also of variable form, and are described as fossae, pits, depressions, grooves, 
furrows, fissures, notches, etc. These non-articular eminences and depressions serve 
to increase the extent of surface for the attachment of ligaments and muscles, and 
are usually well-marked in proportion to the muscularity of the subject. A short 
perforation is called a foramen, a longer passage a canal. 

DEVELOPMENT OF THE SKELETON. 

The Skeleton. — The skeleton is of mesodermal origin, and may be divided into 
(a) that of the trunk (axial skeleton), comprising the vertebral column, skull, ribs, 
and sternum, and (h) that of the limbs (appendicular skeleton). 

The Vertebral Column. — The notochord (Fig. 19) is a temporary structure and 
forms a central axis, around which the segments of the vertebral column are devel- 
oped.^ It is derived from the entoderm, and consists of a rod of cells, M'hich lies 
on the ventral aspect of the neural tube and reaches from the anterior end of the 
mid-brain to the extremity of the tail. On either side of it is a column of paraxial 
mesoderm which becomes subdivided into a number of more or less cubical seg- 
ments, the primitive segments (Figs. 19 and 20). These are separated from one 
another by intersegmental septa and are arranged symmetrically on either side of 
the neural tube and notochord: to every segment a spinal nerve is distributed. 
At first each segment contains a central cavity, the myoccel, but this is soon filled 
with a core of angular and spindle-shaped cells. The cells of the segment become 
differentiated into three groups, which form respectively the cutis-plate or derma- 
tome, the muscle-plate or myotome, and the sclerotome (Fig. 64). The cutis-plate 
is placed on the lateral and dorsal aspect of the myocoel, and from it the true skin 
of the corresponding segment is derived; the muscle-plate is situated on the medial 
side of the cutis-plate and furnishes the muscles of the segment. The cells of the 
sclerotome are largely derived from those forming the core of the myocoel, and lie 
next the notochord. Fusion of the individual sclerotomes in an antero-posterior 
direction soon takes place, and thus a continuous strand of cells, the sclerotogenous 
layer, is formed along the ventro-lateral aspects of the neural tube. The cells of 
this layer proliferate rapidly, and extending medialward surround the notochord; 
at the same time they grow backward on the lateral aspects of the neural tube 
and eventually surround it, and thus the notochord and neural tube are enveloped 

' In the amphioxus the notochord persists and forms the only representative of a skeleton in that animal. 



DEVELOPMENT OF THE SKELETON 



81 



by a continuous sheath of mesoderm, which is termed the membranous vertebral 
colimin. In this mesoderm the original segments are still distinguishable, but each 
is now differentiated into 
two portions, an anterior, 
consisting of loosely arranged 
cells, and a posterior, of 
more condensed tissue (Fig. 
65, A and B) . Between the 
two portions the rudiment 
of the intervertebral fibro- ^•'^• 
cartilage is laid down (Fig. 
65, C). Cells from the pos- 
terior mass grow into the 
intervals between the myo- 
tomes (Fig. 65, B and C) of 
the corresponding and suc- 
ceeding segments, and extend 
both dorsally and ventrally; 
the dorsal extensions sur- 
round the neural tube and 
represent the future verte- 
bral arch, while the ventral 
extend into the body-wall 
as the costal processes. The 
hinder part of the posterior 
mass joins the anterior mass 
of the succeeding segment 
to form the vertebral body. 
Each vertebral body is there- 
fore a composite of two segments, being formed from the posterior portion of 
one segment and the anterior part of that immediately behind it. The vertebral 




Fig. G4. — Transverse section of a human embryo of the third week 
to show the difTerentiation of the primitive segment. (Kollmann.) ao. 
Aorta. m.p. Muscle-plate, n.c. Neural canal, sc. Sclerotome, s p. 
cutis-plate. 



Myotome 

j Anterior portion cf sclerotome 
Notochord 

Posterior portion of sclerotome 
Intermyotomic septum 
Costal process 



• ■•* 




T"^ 



• •• 



*•• • 

•v.v- 



• •••' 






Intervertebral 
fibrocartilage 

Notochord 



trum 



<•• • • 
• ••• 



V.VAV.V 



• tff f • 

• « • « e 
»•• •• 

• • • * • 




• • • * • "^ — 






Iv.*.*.?^ 







B 



Fig. 05. — Scheme showing the manner in which each vertebral centrum is developed from portions of two adjacent 

segments. 



and costal arches are derivatives of the posterior part of the segment in front 
of the intersegmental septum with which they are associated. 
6 



82 



OSTEOLOGY 



This stage is succeeded by that of the cartilaginous vertebral column. In the 
fourth week two cartilaginous centers make their appearance, one on either side of 
the notochord; these extend around tlie notochord and form the body of the cartil- 
aginous vertebra. A second pair of cartilaginous foci appear in the lateral parts of 
the vertebral bow, and grow backward on either side of the neural tube to form 
the cartilaginous vertebral arch, and a separate cartilaginous center appears for 
each costal process. By the eighth week the cartilaginous arch has fused with the 
body, and in the fourth month the two halves of the arch are joined on the dorsal 
aspect of the neural tube. The spinous process is developed from the junction of 
the two halves of the vertebral arch. The transverse process grows out from the 
vertebral arch behind the costal process. 

In the upper cervical vertebrae a band of mesodermal tissue connects the ends of 
the vertebral arches across the ventral surfaces of the intervertebral fibrocartilages. 
This is termed the hypochordal bar or brace; in all except the first it is transitory 
and disappears by fusing with the fibrocartilages. In the atlas, however, the entire 
bow persists and undergoes chondrification; it develops into the anterior arch of the 
bone, while the cartilage representing the body of the atlas forms the dens or 
odontoid process which fuses with the body of the second cervical vertebra. 



Anterior 

longitudinal 

ligament 




Posteriorlongitudinal 

ligament 
Cartilaginous end 

of vertebral body 

Niicleus 'pulposv^ 

Intervertebral fibro- 
cartilage 

Slight enlargement 
of notochord in 
the cartilaginous 
vertebral body 



Fig. 66. — Sagittal section through an intervertebral fibrocartilage and adjacent parts of two vertebrae of an advanced 

sheep's embrj'o. (Kolliker.) 



The portions of the notochord which are surrounded by the bodies of the verte- 
brae atrophy, and ultimately disappear, while those which lie in the centers of the 
intervertebral fibrocartilages undergo enlargement, and persist throughout life as 
the central nucleus pulposus of the fibrocartilages (Fig. 66). 

The Ribs. — The ribs are formed from the ventral or costal processes of the 
primitive vertebral bows, the processes extending between the muscle-plates. In 
the thoracic region of the vertebral column the costal processes grow lateralward to 
form a series of arches, the primitive costal arches. As already described, the 
transverse process grows out behind the vertebral end of each arch. It is at first 
connected to the costal process by continuous mesoderm, but this becomes differ- 
entiated later to form the costotransverse ligament; between the costal process 
and the tip of the transverse process the costotransverse joint is formed by 
absorption. The costal process becomes separated from the vertebral bow by the 
development of the costocentral joint. In the cervical vertebroB (Fig. 67) the trans- 
verse process forms the posterior boundary of the foramen trans versarium, while 
the costal process corresponding to the head and neck of the rib fuses with the 



DEVELOPMENT OF THE SKELETON 



83 



body of the vertebra, and forms the antero-lateral boundary of the foramen. The 
distal portions of the primitive costal arches remain undeveloped; occasionally 
the arch of the seventh cervical vertebra undergoes greater development, and by 
the formation of costovertebral joints is separated off as a rib. In the Inmhar 
region the distal portions of the primitive costal arches fail; the proximal portions 
fuse with the transverse processes to form the transverse processes of descriptive 
anatomy. Occasionally a movable rib is developed in connection with the first 
lumbar vertebra. In the sacral region costal processes are developed only in 
connection with the upper three, or it may be four, vertebra; the processes of 
adjacent segments fuse with one another to form the lateral parts of the sacrum. 
The coccygeal vertehrce are devoid of costal processes. 




CERVICAL 




LUMBAR 





THORACIC 



SACRAL 



Fig. 67. — Diagrams showing the portions of the adult vertebrae derived respectively from the bodies, vertebral 
arches, and costal processes of the embryonic vertebrae. The bodies are represented in yellow, the vertebral arches 
in red, and the costal processes in blue. 



The Sternum. — The ventral ends of the ribs become united to one another by a 
longitudinal bar termed the sternal plate, and opposite the first seven pairs of ribs 
these sternal plates fuse in the middle line to form the manubrium and body of the 
sternum. The xiphoid process is formed by a backward extension of the sternal 
plates. 

The Skull. — Up to a certain stage the development of the skull corresponds with 
that of the vertebral column ; but it is modified later in association with the expan- 
sion of the brain-vesicles, the formation of the organs of smell, sight, and hearing, 
and the development of the mouth and pharynx. 



84 



OSTEOLOGY 




Fossa 
hypophyseos 



ParacJwrdal 
cartilage 



The notochord extends as far forward as the anterior end of the mid-brain, and 
becomes partly surrounded by mesoderm (F'ig. 68) . The posterior part of this meso- 
dermal investment corresponds with the basilar part of the occipital bone, and shows 
a subdivision into four segments, which are separated by the roots of the hypo- 
glossal nerve. The mesoderm then extends over the brain-vesicles, and thus the 

entire brain is enclosed by a mesodermal 
investment, which is termed the membran- 
ous cranium. From the inner layer of this 
the bones of the skull and the membranes 
of the brain are developed; from the outer 
layer the muscles, bloodvessels, true skin, 
and subcutaneous tissues of the scalp. In 
the shark and dog-fish this membranous 
cranium undergoes complete chondrifi- 
cation, and forms the cartilaginous skull 
or chondrocranium of these animals. In 
mammals, on the other hand, the process 
of chondrification is limited to the base 
of the skull — the roof and sides being 
covered in by membrane. Thus the bones 
of the base of the skull are preceded by 
cartilage, those of the roof and sides 
by membrane. The posterior part of the 
base of the skull is developed around 
the notochord, and exhibits a segmented 
condition analogous to that of the vertebral column, while the anterior part arises 
in front of the notochord and shows no regular segmentation. The base of the skull 
may therefore be divided into (a) a chordal or vertebral, and (h) a prechordal or 
prevertebral portion. 



Mesoderm of base 
of skull 

Notochord 



Anterior arch of atlas 

Notochord 
Body of axis 

Third cervical 
vertebra 




Fig. 



68. — Sagittal section of cephalic end of noto- 
chord. (Keibel.) 



Situation of olfactory pit 



Ethmoid plate 
aiid nasal Olfactory organ 
septum^ 



Fossa 
hypophyseos 



Trabecula__ 
cranii 

Situation of 
auditory . 
vesicle 
Parachordal ' 
cartilage 
Notochord'" 




Extension around 
7 olfactory organ 
Foramina for 
olfactory nerves 

Eyeball 

Fossa 
hypophyseos 



--Basilar plate 
--Auditory vesicle 

-'Notochord 



Fig. 69. — Diagrams of the cartilaginous cranium. (Wiedersheim. 



In the lower vertebrates two pairs of cartilages are developed, viz., a pair of 
parachordal cartilages, one on either side of the notochord; and a pair of pre- 
chordal cartilages, the trabeculse cranii, in front of the notochord (Fig. 60). The 
parachordal cartilages (Fig. ()9) unite to form a basilar plate, from which the car- 
tilaginous part of the occipital bone and the basi-sphenoid are developed. On the 
lateral aspects of the parachordal cartilages the auditory vesicles are situated, 



DEVELOPMENT OF THE SKELETON 



85 



and the mesoderm enclosing them is soon converted into cartilage, forming the 
cartilaginous ear-capsules. These cartilaginous ear-capsules, which are of an oval 
shape, fuse with the sides of the basilar plate, and from them arise the petrous 
and mastoid, portions of the temporal bones. The trabeculse cranii (Fig. 69) are 
two curved bars of cartilage which embrace the hypophysis cerebri; their posterior 
ends soon unite with the basilar plate, while their anterior ends join to form the 
ethmoidal plate, which extends forward between the fore-brain and the olfactory 
pits. Later the trabeculae meet and fuse below the hypophysis, forming the floor 



Crista galli 



Cribriform plate 



Meckel's cartilage 
Malleus 

Inciis 

Int. acoristic meat. 
Jug ula r Jorame n 
Fossa svbarcuata t 




Small wing of sphenoid 
Optic foramen 



Great wing of 

sphenoid 



Sella turcica 
Dorsum selloe 



Canal for facial 
nerve 

Ear capsule 



Ductus endol. 



Canal for hypoglossal nerve 



Foramen magnum 

Fig. 70. — Model of the chondrocranium of a human embryo, 8 cm. long. (Hertwig.) The membrane bones are 

not represented. 

of the fossa hypophyseos and so cutting off the anterior lobe of the hypophysis 
from the stomodeum. The median part of the ethmoidal plate forms the bony 
and cartilaginous parts of the nasal septum. P>om the lateral margins of the 
trabecular cranii three processes grow out on either side. The anterior forms the 
ethmoidal labyrinth and the lateral and alar cartilages of the nose; the middle 
gives rise to the small wing of the sphenoid, while from the posterior the great 
wing and lateral pterygoid plate of the sphenoid are developed (Figs. 70, 71). 
The bones of the vault are of membranous formation, and are termed dermal or 
covering bones. They are partly developed from the mesoderm of the membranous 



86 



OSTEOLOGY 



cranium, and partly from that which Hes outside the entoderm of the fore- 
gut. They comprise the upper part of the occipital squama (interparietal), the 
squamse and tympanic parts of the temporals, the parietals, the frontal, the vomer, 
the medial pterygoid plates, and the bones of the face. Some of them remain 
distinct throughout life, e. g., parietal and frontal, while others join with the bones 
of the chondrocranium, e. g., interparietal, squama? of temporals, and medial 
pterygoid plates. 

Recent observations have shown that, in mammals, the basi-cranial cartilage, 
both in the chordal and prechordal regions of the base of the skull, is developed 
as a single plate which extends from behind forward. In man, however, its posterior 
part shows an indication of being developed from two chondrifying centers which 
fuse rapidly in front and below. The anterior and posterior thirds of the cartilage 
surround the notochord, but its middle third lies on the dorsal aspect of the noto- 
chord, which in this region is placed between the cartilage and the wall of the 
pharynx. 



Optic foramen Small wing of sphenoid 



Great wing of sphenoid 



Nasal 
capsule 

Sept. 
nasi 



Maxilla 



Palatine 
bone 




Vomer 



Mandible 



Cricoid cart 

Thyroid cart 



Styloid process 
Fen. cocMeoB 



Canal for hypoglossal 
nerve 



Fia. 71. — The same model as shown in Fig. 70 from the left side. Certain of the membrane bones of the right side 

are represented in yellow. (Hertwig.) 



BONE 

Structure and Physical Properties. — Bone is one of the hardest structures of 
the animal body; it possesses also a certain degree of toughness and elasticity. 
Its color, in a fresh state, is pinkish-white externally, and deep red within. On 
examining a section of any bone, it is seen to be composed of two kinds of tissue, 
one of which is dense in texture, like ivory, and is termed compact tissue; the other 
consists of slender fibers and lamellae, which join to form a reticular structure; 
this, from its resemblance to lattice-work, is called cancellous tissue. The compact 
tissue is always placed on the exterior of the bone, the cancellous in the interior. 
The relative quantity of these two kinds of tissue varies in different bones, and 
in different parts of the same bone, according as strength or lightness is requisite. 
Close examination of the compact tissue shows it to be extremely porous, so that 
the difference in structure between it and the cancellous tissue depends merely 
upon the different amount of solid matter, and the size and number of spaces in 
each; the cavities are small in the compact tissue and the solid matter between 



BONE 



87 



them abundant, while in the cancellous tissue the spaces are large and the solid 
matter is in smaller quantity. 

Bone during life is permeated by vessels, and is enclosed, except where it is 
coated with articular cartilage, in a fibrous membrane, the periosteum, by means 
of which many of these vessels reach the hard tissue. If the periosteum be stripped 
from the surface of the living bone, small bleeding points are seen which mark the 
entrance of the periosteal vessels; and on section during life every part of the 
bone exudes blood from the minute vessels which ramify in it. The interior of 
each of the long bones of the limbs presents a cylindrical cavity filled w4th marrow 
and lined by a highly vascular areolar structure, called the medullary membrane. 



Thf, Strength 


OF Bone Compared 


WITH OTHER MATERIALS 




Substance. 




Weight in 
pounds per 
cubic foot. 


Ultimate strength. 
Pounds per square inch. 




Tension. 


Compression. 


Shear. 


Medium steel 


490 

170 

46 


65,000 
1,.500 
12,5001 
13,2001 
17,7001 


60,000 
15,000 
7,0001 
18,0001 
24,0001 


40,000 
2,000 
4,0002 

11,800'i 
7,1501 


Granite 


Oak, white 


Compact bone (low) . . / . 
Compact bone (high) 


119 



Periosteum.— The periosteum adheres to the surface of each of the bones in 
nearly every part, but not to cartilaginous extremities. When strong tendons or 
ligaments are attached to a bone, the periosteum is incorporated with them. It 
consists of two layers closely united together, the outer one formed chiefly of 
connective tissue, containing occasionally a few fat cells; the inner one, of elastic 
fibers of the finer kind, forming dense membranous networks, which again can be 
separated into several layers. In young bones the periosteum is thick and very 
vascular, and is intimately connected at either end of the bone with the epiphysial 
cartilage, but less closely with the body of the bone, from which it is separated by 
a layer of soft tissue, containing a number of granular corpuscles or osteoblasts, by 
which ossification proceeds on the exterior of the young bone. Later in life the 
periosteum is thinner and less vascular, and the osteoblasts are converted into an 
epithelioid layer on the deep surface of the periosteum. The periosteum serves 
as a nidus for the ramification of the vessels previous to their distribution in the 
bone; hence the liability of bone to exfoliation or necrosis when denuded of this 
membrane by injury or disease. Fine nerves and lymphatics, w^hich generally 
accompany the arteries, may also be demonstrated in the periosteum. 

Marrow. — The marrow not only fills up the cylindrical cavities in the bodies of 
the long bones, but also occupies the spaces of the cancellous tissue and extends 
into the larger bony canals (Haversian canals) which contain the bloodvessels. 
It differs in composition in different bones. In the bodies of the long bones the 
marrow is of a yellow color, and contains, in 100 parts, 96 of fat, 1 of areolar tissue 
and vessels, and 3 of fluid with extractive matter; it consists of a basis of connective 
tissue supporting numerous bloodvessels and cells, most of which are fat cells 
but some are "marrow cells," such as occur in the red marrow to be immediately 
described. In the flat and short bones, in the articular ends of the long bones, 
in the bodies of the vertebrae, in the cranial diploe, and in the sternum and ribs 
the marrow is of a red color, and contains, in 100 parts, 75 of water, and 25 of solid 
matter consisting of cell-globulin, nucleoprotein, extractives, salts, and only a 
small proportion of fat. The red marrow consists of a small quantity of connective 
tissue, bloodvessels, arid numerous cells (Fig. 72), some few of which are fat cells, 

' Indicates stresses with the grain, i. e., when the load is parallel to the long axis of the material, or parallel to the 
direction of the fibers of the material. 

2 Indicates unit-stresses across the grain, i. c, at right angles to the direction of the fibers of the material. 



88 



OSTEOLOGY 



but the great majority are roundish nucleated cells, the true "marrow cells" 
of KoUiker. These marrow cells proper, or myelocytes, resemble in appearance 
lymphoid corpuscles, and like them are ameboid; they generally have a hyaline 
protoplasm, though some show granules either oxyphil or basophil in reaction. 
A number of eosinophil cells are also present. Among the marrow cells may be 
seen smaller cells, which possess a slightly pinkish hue; these are the erythroblasts 
or normoblasts, from which the red corpuscles of the adult are derived, and which 
may be regarded as descendants of the nucleated colored corpuscles of the embryo. 
Giant cells {mycloplazes , osteoclasts), large, multinucleated, protoplasmic masses, 
are also to be found in both sorts of adult marrow, but more particularly in red 
marrow. They were believed by Kolliker to be concerned in the absorption of 
bone matrix, and hence the name which he gave to them — osteoclasts. They 
excavate in the bone small shallow pits or cavities, which are named Howship's 
foveolae, and in these they are found lying. 



Normoblast with dividing nucleus 



Myelocyte — -~M 



Erythrocyte - 



Myeloflaxe -^-jn-i- 



Myelocyte 



Fat- 




__ Eosinophil 
cell 



iJS^ Normoblasts 



Myelocyte 
dividing 

Myelocyte 



Fat 



Fig. 72. — Human bone marrow. Highly magnified. 



Vessels and Nerves of Bone. — The bloodvessels of bone are very numerous. Those 
of the compact tissue are derived from a close and dense network of vessels ramify- 
ing in the periosteum. From this membrane vessels pass into the minute orifices 
in the compact tissue, and run through the canals which traverse its substance. 
The cancellous tissue is supplied in a similar way, but by less numerous and larger 
vessels, which, perforating the outer compact tissue, are distributed to the cavities 
of the spongy portion of the bone. In the long bones, numerous apertures may 
be seen at the ends near the articular surfaces; some of these give passage to the 
arteries of the larger set of vessels referred to; but the most numerous and largest 
apertures are for some of the veins of the cancellous tissue, which emerge apart 
from the arteries. The marrow in the body of a long bone is supplied by one 
large artery (or sometimes more), which enters the bone at the nutrient foramen 
(situated in most cases near the center of the body), and perforates obliquely the 
compact structure. The medullary or nutrient artery, usually accompanied by one 
or two veins, sends branches upward and downward, which ramify in the medul- 
lary membrane, and give twigs to the adjoining canals. The ramifications of this 



BONE 



89 



vessel anastomose with the arteries of the cancellous and compact tissues. In most 
of the flat, and in many of the short spongy bones, one or more large apertures are 
observed, which transmit to the central parts of the bone vessels corresponding to 
the nutrient arteries and veins. The veins emerge from the long bones in three 
places (KoUiker): (1) one or two large veins accompany the artery; (2) numerous 
large and small veins emerge at the articular extremities; (3) many small veins 
pass out of the compact substance. In the flat cranial bones the veins are large, 
very numerous, and run in tortuous canals in the diploic tissue, the sides of the 
canals being formed by thin lamellae of bone, perforated here and there for the 
passage of branches from the adjacent cancelli. The same condition is also 
found in all cancellous tissue, the veins being enclosed and supported by osseous 
material, and having exceedingly thin coats. When a bone is divided, the vessels 
remain patulous, and do not contract in the canals in which they are contained. 
Lymphatic vessels, in addition to those found in the periosteum, have been traced 
by Cruikshank into the substance of bone, and Klein describes them as running in 
the Haversian canals. Nerves are distributed freely to the periosteum, and accom- 
pany the nutrient arteries into the interior of the bone. They are said by Kolliker 
to be most numerous in the articular extremities of the long bones, in the vertebrae, 
and in the larger flat bones. 




Fig. 73. — Transverse section of compact tissue bone. Magnified. (Sharpey.) 

Minute Anatomy. — A transverse section of dense bone may be cut with a saw 
and ground down until it is sufficiently thin. 

If this be examined with a rather low power the bone will be seen to be mapped 
out into a number of circular districts each consisting of a central hole surrounded 
by a number of concentric rings. These districts are termed Haversian systems; 
the central hole is an Haversian canal, and the rings are layers of bony tissue 
arranged concentrically around the central canal, and termed lamellae. More- 
over, on closer examination it will be found that between these lamellae, and 
therefore also arranged concentrically around the central canal, are a number of 
little dark spots, the lacunae, and that these lacunae are connected with each other 
and with the central Haversian canal by a number of fine dark lines, which radiate 
like the spokes of a wheel and are called canalicuU. Filling in the irregular intervals 
which are left between these circular systems are other lamellae, with their lacunae 
and canaliculi running in various directions, but more or less curved (Fig. 73); 
they are termed interstitial lamellae. Again, other lamellae, found on the surface 
of the bone, are arranged parallel to its circumference; they are termed circum- 



90 



OSTEOLOGY 



ferential, or by some authors primary or fundamental lamellae, to distinguish them 
from those laid down around the axes of the Haversian canals, which are then 
termed secondary or special lamellae. 

The Haversian canals, seen in a transverse section of bone as round holes at or 
about the center of each Haversian system, may be demonstrated to be true canals 
if a longitudinal section be made (Fig. 74). It will then be seen that the canals 
run parallel with the longitudinal axis of the bone for a short distance and then 
branch and communicate. They vary considerably in size, some being as much as 
0.12 mm. in diameter; the average size is, however, about 0.05 mm. Near the 
medullary cavity the canals are larger than those near the surface of the bone. 
Each canal contains one or two bloodvessels, with a small quantity of delicate 
connective tissue and some nerve filaments. In the larger ones there are also 
lymphatic vessels, and cells with branching processes which communicate, through 
the canalculi, with the branched processes of certain bone cells in the substance 
of the bone. Those canals near the surface of the bone open upon it by minute 
orifices, and those near the medullary cavity open in the same way into this space, 
so that the whole of the bone is permeated by a system of bloodvessels running 
through the bony canals in the centers of the Haversian systems. 

The lamellae are thin plates of bony tissue 
encircling the central canal, and may be com- 
pared, for the sake of illustration, to a number 
of sheets of paper pasted one over another 
around a central hollow cylinder. After 
macerating a piece of bone in dilute mineral 
acid, these lamellae may be stripped off in a 





Via. 74. — Section parallel to the surface 
from the body of the femur. X 100. a. Haver- 
sian canals; 6, lacunse seen from the side; c, 
others seen from the surface in lamellse, which 
are cut horizontally. 



Fio. 75. — Perforating fibers, human parietal bone, decalcified. 
(H. Miiller.) a, perforating fibers in situ; b, fibres drawn out of 
their sockets; c, sockets. 



longitudinal direction as thin films. If one of these be examined with a high power 
of the microscope, it will be found to be composed of a finely reticular structure, 
made up of very slender transparent fibers, decussating obliquely; and coalescing 
at the points of intersection ; these fibers are composed of fine fibrils identical with 
those of white connective tissue. The intercellular matrix between the fibers is 
impregnated by calcareous deposit which the acid dissolves. In many places the 
various lamellae may be seen to be held together by tapering fibers, which run 
obliquely through them, pinning or bolting them together; they were first de- 
scribed by Sharpey, and were named by him perforating fibers (Fig. 75). 

The Lacunae are situated between the lamellse, and consist of a number of oblong 




BONE 91 

spaces. In an ordinary microscopic section, viewed by transmitted light, they 
appear as fusiform opaque spots. Each lacuna is occupied during life by a branched 
cell, termed a bone-cell or bone-corpuscle, the processes from which extend into the 
canaliculi (Fig. 70). 

The CanaUcuU are exceedingly minute channels, crossing the lamellae and con- 
nectmg the lacunae with neighboring lacunae and also with the Haversian canal. 
From the Haversian canal a number of canaliculi are given off, which radiate from 
it, and open into the first set of lacunte between the first and second lamellae. 
From these lacunae a second set of canaliculi is given off; these run outward to the 
next series of lacunae, and so on until the periphery of the Haversian system is 
reached; here the canaliculi given off from the last series of lacuna? do not communi- 
cate with the lacunae of neighboring Haversian systems, but after passing outward 
for a short distance form loops and return to their own lacunar. Thus every 
part of an Haversian system is supplied with nutrient fluids derived from the 
vessels in the Haversian canal and distributed 
through the canaliculi and lacunae. 

The bone cells are contained in the lacunae, 
which, however, they do not completely fill. 
They are flattened nucleated branched cells, 
homologous with those of connective tissue; the 
branches, especially in young bones, pass into 
the canaliculi from the lacunae. 

In thin plates of bone (as in the walls of 
the spaces of cancellous tissue) the Haversian 
canals are absent, and the canaliculi open into 
the spaces of the cancellous tissue (medullary 
spaces), which thus have the same function as 

the Haversian canals. ^^°- 76.— Nucleated bone cells and their 

_ _ . processes, contained in the bone lacuna and 

Chemical Composition. Bone consists of an t^elr canalicull respectively. From a section 

I I , ... through the vertebra of an adult mouse. 

animal and an earthy part intimately com- (Kiein and Nobie smith.) 
bined together. 

The animal part may be obtained by immersing a bone for a considerable time 
in dilute mineral acid, after which process the bone comes out exactly the same 
shape as before, but perfectly flexible, so that a long bone (one of the ribs, for 
example) can easily be tied in a knot. If now a transverse section is made 
(Fig. 77) the same general arrangement of the Haversian canals, lamellae, lacunae, 
and canaliculi is seen. 

The earthy part may be separately obtained by calcination, by which the 
animal matter is completely burnt out. The bone will still retain its original 
form, but it will be white and brittle, will have lost about one-third of its original 
weight, and will crumble down with the slightest force. The earthy matter is 
composed chiefly of calcium phosphate, about 58 per cent, of the weight of the 
bone, calcium carbonate about 7 per cent., calcium fluoride and magnesium phos- 
phate from 1 to 2 per cent, each and sodium chloride less than 1 per cent. ; they confer 
on bone its hardness and rigidity, while the animal matter {ossein) determines its 
tenacity. 

Ossification. — Some bones are preceded by membrane, such as those forming 
the roof and sides of the skull; others, such as the bones of the limbs, are preceded 
by rods of cartilage. Hence two kinds of ossification are described: the intra- 
membranous and the intracartilaginous. 

Intramembranous Ossification. — In the case of bones which are developed 
in membrane, no cartilaginous mould precedes the appearance of the bony tissue. 
The membrane which occupies the place of the future bone is of the nature of con- 
nective tissue, and ultimately forms the periosteum; it is composed of fibers and 
granular cells in a matrix. The peripheral portion is more fibrous, while, in the 



92 



OSTEOLOGY 



interior the cells or osteoblasts predominate; the whole tissue is richly supplied with 
bloodvessels. At the outset of the process of bone formation a little network 
of spicules is noticed radiating from the point or center of ossification. These 
rays consist at their growing points of a network of fine clear fibers and granular 




Fig. 



Haversian canal 

Bone corpuscle Bone corpuscle 
between inter- 
stitial lainellm 

'7. — Transverse section of body of human fibula, decalcified. X 250. 



corpuscles with an intervening ground substance (Fig. 78). The fibers are termed 
osteogenetic fibers, and are made up of fine fibrils diftering little from those of white 
fibrous tissue. The membrane soon assumes a dark and granular appearance from 
the deposition of calcareous granules in the fibers and in the intervening matrix, 



Union of 
adjacent ~" 
spicules 



Osteoblasts'. 




Osteogenetic 

fibers 



Calcified deposit 

~ ~ between the fibers 



Bony spicules 



Fig. 78. — Part of the growing edge of the developing parietal bone of a fetal cat. (After J. Lawrence.) 

and in the calcified material some of the granular corpuscles or osteoblasts are 
enclosed. By the fusion of the calcareous granules the tissue again assumes a 
more transparent appearance, but the fibers are no longer so distinctly seen. 
The involved osteoblasts form the corpuscles of the future bone, the spaces in 



BONE 



93 



9, ' 










^^^ 






which they are enclosed constituting the lacunae. As the osteogenetic fibers grow 
out to the periphery they continue to calcify, and give rise to fresh bone spicules. 
Thus a network of bone is formed, the meshes of which contain the bloodvessels 
and a delicate connective tissue crowded with osteoblasts. The bony trabeculae 
thicken by the addition of fresh layers of bone formed by the osteoblasts on their 
surface, and the meshes are correspondingly encroached upon. Subsequently 
successive layers of bony tissue are deposited under the periosteum and around 
the larger vascular channels which become the Haversian canals, so that the bone 
increases much in thickness. 

Intercartilaginous Ossification. — Just before ossification begins the mass is 
entirely cartilaginous, and in a long bone, which may be taken as an example, the 
process commences in the center and proceeds toward the extremities, which for 
some time remain cartilaginous. Subsequently a similar process commences in 
one or more places in those extremities and gradually extends through them. 
The extremities do not, however, become joined to the body of the bone by bony 
tissue until growth has ceased; between the body and either extremity a layer of 
cartilaginous tissue termed the epiphysial cartilage persists for a definite period. 

The first step in the ossification of 
the cartilage is that the cartilage cells, 
at the point where ossification is com- 
mencing and which is termed a center 
of ossification, enlarge and arrange 
themselves in rows (Fig. 79). The 
matrix in which they are imbedded 
increases in quantity, so that the cells 
become further separated from each 
other. A deposit of calcareous material 
now takes place in this matrix, between 
the rows of cells, so that thev become 
separated from each other by longi- 
tudinal columns of calcified matrix, 
presenting a granular and opaque ap- 
pearance. Here and there the matrix 
between two cells of the same row also 
becomes calcified, and transverse bars 
of calcified substance stretch across 
from one calcareous column to another. 
Thus there are longitudinal groups of 
the cartilage cells enclosed in oblong 
cavities, the walls of which are formed 
of calcified matrix which cuts off all 
nutrition from the cells; the cells, in 
consequence, atrophy, leaving spaces 
called the primary areolae. 

At the same time that this process 
is going on in the center of the solid 
bar of cartilage, certain changes are 
taking place on its surface. This is 
covered by a very vascular membrane, 
the perichondrium, entirely similar to the 
embryonic connective tissue already 
described as constituting the basis of 
membrane bone; on the inner surface of this — that is to say, on the surface in 
contact with the cartilage — are gathered the formative cells, the osteoblasts. By 
the agency of these cells a thin layer of bony tissue is formed between the peri- 






FiG. 79. — Section of fetal bone of cat. ir. Irruption 
of the subperiosteal tissue, p. Fibrous layer of the perios- 
teum. 0. Layer of osteoblasts, im. Subperiosteal bony 
deposit. (From Quain's "Anatomy," E. A. Schafer.) 



94 



OSTEOLOGY 



chondrium and the cartilage, by the intramemhranous mode of ossification just 
described. There are then, in this first stage of ossification, two processes going 
on simultaneously: in the center of the cartilage the formation of a number of 
oblong spaces, formed of calcified matrix and containing the withered cartilage 
cells, and on the surface of the cartilage the formation of a layer of true mem- 
brane bone. The second stage consists in the prolongation into the cartilage of 
processes of the deeper or osteogenetic layer of the perichondrium, which has 
now become periosteum (Fig. 79, ir). The processes consist of bloodvessels and 
cells — osteoblasts, or bone-formers, and osteoclasts, or bone-destroyers. The latter 
are similar to the giant cells (myeloplaxes) found in marrow, and they excavate 
passages through the new-formed bony layer by absorption, and pass through 
it into the calcified matrix (Fig. 80). Wherever these processes come in con- 
tact with the calcified walls of the primary areolae they absorb them, and thus 
cause a fusion of the original cavities and the formation of larger spaces, which 
are termed the secondary areolae or medullary spaces. These secondary spaces 
become filled with embryonic marrow, consisting of osteoblasts and vessels, derived, 

in the manner described above, from the 
osteogenetic layer of the periosteum (Fig. 80). 
Thus far there has been traced the forma- 
tion of enlarged spaces (secondary areolae), 
the perforated walls of which are still formed 
by calcified cartilage matrix, containing an 
embryonic marrow derived from the processes 
sent in from the osteogenetic layer of the 
periosteum, and consisting of bloodvessels and 
osteoblasts. The walls of these secondary 
areolae are at this time of only inconsiderable 
thickness, but they become thickened by the 
deposition of layers of true bone on their sur- 
face. This process takes place in the follow- 
ing manner: Some of the osteoblasts of the 
embryonic marrow, after undergoing rapid 
division, arrange themselves as an epithelioid 
layer on the surface of the wall of the space 
(P'ig. 81). This layer of osteoblasts forms a 
bony stratum, and thus the wall of the space 
becomes gradually covered with a layer of 



Osteoclasts- '^^ 




Fig. 80. — Part of a longitudinal section of 
the developing femur of a rabbit, a. Flattened 
cartilage cells, b. Enlarged cartilage cells, c, 
d. Newly formed bone. e. Osteoblasts. /. 
Giant cells or osteoclasts. g, h. Shrunken 
cartilage cells. (From ' 'Atlas of Histology, " 
Klein and Noble Smith.) 



Osteoblasts 




fl'^f-f.>7 rdUKr:, 



^^^^'^z^nx-rmm^p^^^^^ 



Fig. 81. — Osteoblasts and osteoclasts on trabecula of lower jaw of 
calf embryo. (KoUiker.) 



true osseous substance in which some of the bone-forming cells are included as 
bone corpuscles. The next stage in the process consists in the removal of these 
primary bone spicules by the osteoclasts. One of these giant cells may be found 
lying in a Howship's foveola at the free end of each spicule. The removal of the 



BONE 95 

primary spicules goes on jpari passu with the formation of permanent bone by 
the periosteum, and in this way the medullary cavity of the body of the bone is 
formed. 

This series of changes has been gradually proceeding toward the end of the body 
of the bone, so that in the ossifying bone all the changes described above may 
be seen in different parts, from the true bone at the center of the body to the hyaline 
cartilage at the extremities. 

While the ossification of the cartilaginous body is extending toward the articular 
ends, the cartilage immediately in advance of the osseous tissue continues to grow 
until the length of the adult bone is reached. 

During the period of growth the articular end, or epiphysis, remains for some 
time entirely cartilaginous, then a bony center appears, and initiates in it the 
process of intracartilaginous ossification; but this process never extends to any 
great distance. The epiphysis remains separated from the body by a narrow 
cartilaginous layer for a definite time. This layer ultimately ossifies, the distinc- 
tion between body and epiphysis is obliterated, and the bone assumes its completed 
form and shape. The same remarks also apply to such processes of bone as are 
separately ossified, e. g., the trochanters of the femur. The bones therefore con- 
tinue to grow until the body has acquired its full stature. They increase in length 
by ossification continuing to extend behind the epiphysial cartilage, which goes 
on growing in advance of the ossifying process. They increase in circumference 
by deposition of new bone, from the deeper layer of the periosteum, on their exter- 
nal surface, and at the same time an absorption takes place from within, by which 
the medullary cavities are increased. 

The permanent bone formed by the periosteum when first laid down is cancellous 
in structure. Later the osteoblasts contained in its spaces become arranged in 
the concentric layers characteristic of the Haversian systems, and are included 
as bone corpuscles. 

The number of ossific centers ^•a^ies in different bones. In most of the short 
bones ossification commences at a single point near the center, and proceeds toward 
the surface. In the long bones there is a central point of ossification for the body 
or diaph}'sis: and one or more for each extremity, the epiphysis. That for the 
body is the first to appear. The times of union of the epiphyses with the body 
vary inversely with the dates at which their ossifications began (with the exception 
of the fibula) and regulate the direction of the nutrient arteries of the bones. Thus, 
the nutrient arteries of the bones of the arm and forearm are directed toward 
the elbow, since the epiphyses at this joint become united to the bodies before 
those at the opposite extremities. In the lower limb, on the other hand, the 
nutrient arteries are directed away from the knee: that is, upward in the femur, 
downward in the tibia and fibula; and in them it is observed that the upper epiphysis 
of the femur, and the lower epiphyses of the tibia and fibula, unite first with the 
bodies. Where there is only one epiphysis, the nutrient artery is directed toward 
the other end of the bone; as toward the acromial end of the clavicle, toward the 
distal ends of the metacarpal bone of the thumb and the metatarsal bone of the 
great toe, and toward the proximal ends of the other metacarpal and metatarsal 
bones. 

Parsons^ groups epiphyses under three headings, viz.: (1) pressure epiphyses, 
appearing at the articular ends of the bones and transmitting "the weight of the 
body from bone to bone;" (2) traction epiphyses, associated with the insertion 
of muscles and "originally sesamoid structures though not necessarily sesamoid 
bones;" and (3) atavistic epiphyses, representing parts of the skeleton, which at 
one time formed separate bones, but which have lost their function, "and only 
appear as separate ossifications in early life." 

' Jour, of Anat. and Phys., vols, zxxviii, xsxix, and xlii. 



96 



OSTEOLOGY 



THE VERTEBRAL COLUMN (COLUMNA VERTEBRALIS ; SPINAL 

COLUMN). 

The vertebral column is a flexuous and flexible column, formed of a series oi 
bones called vertebrae. 

The vertebrae are thirty-three in number, and are grouped under the names 
cervical, thoracic, lumbar, sacral, and coccygeal, according to the regions they 
occupy; there are seven in the cervical region, twelve in the thoracic, five in the 
lumbar, five in the sacral, and four in the coccygeal. 

This number is sometimes increased by an additional vertebra in one region, 
or it may be diminished in one region, the deficiency often being supplied by an 
additional vertebra in another. The number of cervical vertebra is, however, 
very rarely increased or diminished. 

The vertebrae in the upper three regions of the column remain distinct through- 
out life, and are known as true or movable vertebrae; those of the sacral and 
coccygeal regions, on the other hand, are termed false or fixed vertebrae, because 
they are united with one another in the adult to form two bones — fi^'e forming 
the upper bone or sacrum, and four the terminal bone or coccyx. 

With the exception of the first and second cervical, the true or movable vertebrae 
present certain common characteristics which are best studied by examining one 
from the middle of the thoracic region. 



GENERAL CHARACTERISTICS OF A VERTEBRA. 

A typical vertebra consists of two essential parts — viz., an anterior segment, the 
body, and a posterior part, the vertebral or neural arch; these enclose a foramen, 
the vertebral foramen. The vertebral arch consists of a pair of pedicles and a pair 
of laminae, and supports seven processes — viz., four articular, two transverse, and 
one spinous. 



Costal fovea ■ S 



Pedicle or roo' of 
vertebral arch 




Lami 



ina 



II 



ISuperwr articular process 



Fig. 82. — A typical thoracic vertebra, viewed from above. 

^Mien the vertebrae are articulated with each other the bodies form a strong 
pillar for the support of the head and trunk, and the vertebral foramina constitute 
a canal for the protection of the medulla spinalis (spinal cord), while between 
every pair of vertebrae are two apertures, the intervertebral foramina, one on 
either side, for the transmission of the spinal nerves and vessels. 

Body {corpus rertebrcp). — The body is the largest part of a vertebra, and is 
more or less cylindrical in shape. Its upper and lower surfaces are flattened and 



THE CERVICAL VERTEBRJE 



97 



rough, and give attachment to the intervertebral fibrocartilages, and each presents 
a rim around its circumference. In front, the body is convex from side to side 
and concave from above downward . Behind, it is flat from above downward 
and slightly concave from side to side. Its anterior surface presents a few small 
apertures, for the passage of nutrient vessels; on the posterior surface is a single 
large, irregular aperture, or occasionally more than one, for the exit of the basi- 
vertebral veins from the body of the vertebra. 

Pedicles {radices orci vertebrce). — The pedicles are two short, thick processes, 
which project backward, one on either side, from the upper part of the body, 
at the junction of its posterior and lateral surfaces. The concavities above and 
below the pedicles are named the vertebral notches; and when the vertebrae are 
articulated, the notches of each contiguous pair of bones form the intervertebral 
foramina, already referred to. 

Laminae. — The laminae are two broad plates directed backward and medialward 
from the pedicles. They fuse in the middle line posteriorly, and so complete the 
posterior boundary of the vertebral foramen. Their upper borders and the lower 
parts of their anterior surfaces are rough for the attachment of the ligamenta 
flava. 

Processes. — Spinous Process (processus spinosus). — The spinous process is 
directed backward and downward from the junction of the laminae, and serves 
for the attachment of muscles and ligaments. 

Articular Processes. — ^The articular processes, two superior and two inferior, 
spring from the junctions of the pedicles and laminae. The superior project 
upward, and their articular surfaces are directed more or less backward; the 
inferior project do\\'nward, and their surfaces look more or less forward. The 
articular surfaces are coated with hyaline cartilage. 

Transverse Processes (processus transversi). — The transverse processes, two in 
number, project one at either side from the point where the lamina joins the 
pedicle, between the superior and inferior articular processes. They serve for 
the attachment of muscles and ligaments. 

Structure of a Vertebra (Fig. S3). — The body is composed of cancellous tissue, covered by 
a thin coating of compact bone; the latter is perforated by numerous orifices, some of large size 
for the passage of vessels; the interior of the bone is traversed by one or two large canals, for the 
reception of veins, which converge toward a single large, irregular aperture, or several small 
apertures, at the posterior part of the 
body. The thin bony lamellae of the 
cancellous tissue are more pronounced 
in hnes perpendicular to the upper 
and lower surfaces and are developed 
in response to greater pressure ni this 
direction (Fig. S3). The arch and 
processes projecting from it have 
thick coverings of compact tissue. 

The Cervical Vertebrae (Verte- 
brae Cervicales). 

The cervical vertebrae (Fig. 
84) are the smallest of the true 
vertebrae, and can be readily 

distinguished from those of the thoracic or lumbar regions by the presence of a 
foramen in each transverse process. The first, second, and seventh present excep- 
tional features and must be separately described; the following characteristics are 
common to the remaining four. 

The body is small, and broader from side to side than from before backward 
The anterior and posterior surfaces are flattened and of equal depth; the former 




Fig. 83. — Sagittal section of a lumbar vertebra. 



98 



OSTEOLOGY 



is placed on a lower level than the latter, and its inferior border is prolonged 
downward, so as to overlap the upper and forepart of the vertebra below. The 
upper surface is concave transversely, and presents a projecting lip on either side; 
the lower surface is concave from before backward, convex from side to side, and 
presents laterally shallow concavities which receive the corresponding projecting 
lips of the subjacent vertebra. The pedicles are directed lateralward and backward, 
and are attached to the body midway between its upper and lower borders, so that 
the superior vertebral notch is as deep as the inferior, but it is, at the same time, 



Anterior tubercle of 
transverse 'process 
Foramen 
iransversarium 
Posterior tubercle of—' 
transverse process 




inotis 
process 

Fig. 84. — A cerv-ical vertebra. 



Transverse process 



Superior articular 
process 

Inferior articular 
process 



narrower. The laminae are narrow, and thinner above than below; the vertebral 
foramen is large, and of a triangular form. The spinous process is short and bifid, 
the two divisions being often of unequal size. The superior and inferior articular 
processes on either side are fused to form an articular pillar, which projects lateral- 
ward from the junction of the pedicle and lamina. The articular facets are flat 
and of an o^'al form: the superior look backward, upward, and slightly medial- 
ward: the inferior forward, downward, and slightly lateralward. The transverse 
processes are each pierced by the foramen transversarimn, which, in the upper six 



Body /C 
Anterior tubercle of ^ 
transverse process 



Sulcus for nerve 



Superior articular surface 
Articular pillar 




Fig. 



Posterior tubercle of 
transverse process 

85. — Side view of a typical cervical vertebra. 



Spinalis process 



vertebrae, gives passage to the vertebral artery and vein and a plexus of sympa-. 
thetic nerves. Each process consists of an anterior and a posterior part. The 
anterior portion is the homologue of the rib in the thoracic region, and is there- 
fore named the costal process or costal element: it arises from the side of the bod}'', 
is directed lateralward in front of the foramen, and ends in a tubercle, the anterior 
tubercle. The posterior part, the true transverse process, springs from the 
vertebral arch behind the foramen, and is directed forward and lateralward; it 
ends in a flattened vertical tubercle, the posterior tubercle. These two parts 



THE CERVICAL VERTEBRM 



99 



are joined, outside the foramen, by a bar of bone which exhibits a deep sulcus 
on its upper surface for the passage of the corresponding spinal nerve. ^ 

First Cervical Vertebra.— The first cervical vertebra (Fig. 86) is named the 
atlas because it supports the globe of the head. Its chief peculiarity is that it has 
no body, and this is due to the fact that the body of the atlas has fused with that 
of the next vertebra. Its other peculiarities are that it has no spinous process, 
is ring-like, and consists of an anterior and a posterior arch and two lateral masses. 
The anterior arch forms about one-fifth of the ring: its anterior surface is convex, 
and presents at its center the anterior tubercle for the attachment of the Longus 
colli muscles; posteriorly it is concave, and marked by a smooth, oval or circular 
facet {fovea dentis), for articulation with the odontoid process {dens) of the axis. 
The upper and lower borders respectively give attachment to the anterior atlanto- 
occipital membrane and the anterior atlantoaxial ligament; the former connects 
it with the occipital bone above, and the latter with the axis below. The posterior 
arch forms about two-fifths of the circumference of the ring: it ends behind in the 
posterior tubercle, which is the rudiment of a spinous process and gives origin to 
the Recti capitis posteriores minores. The diminutive size of this process pre- 
vents any interference with the movements between the atlas and the skull. 
The posterior part of the arch presents above and behind a rounded edge for 



Anterior tvhercle 



Tratisverse 
process 



Oxiline of section of odontoid 
process 
Outline of section of trans- 
verse atlanfal ligament 

Foramen 

trayisver- 
sarium 




Groove for vtrichral artery 
and first cervical nerve 



Posterior tubercle 

Fig. 86. — First cer%acal vertebra, or atlas. 



the attachment of the posterior atlantooccipital membrane, while immediately 
behind each superior articular process is a groove {sidcus arterioe vertebralis) , 
sometimes converted into a foramen by a delicate bony spiculum which arches 
backward from the posterior end of the superior articular process. This groove 
represents the superior vertebral notch, and serves for the transmission of the 
vertebral artery, which, after ascending through the foramen in the transverse 
process, winds around the lateral mass in a direction backward and medialward; it 
also transmits the suboccipital (first spinal) nerve. On the under surface of the 
posterior arch, behind the articular facets, are two shallow grooves, the inferior 
vertebral notches. The lower border gives attachment to the posterior atlanto- 
axial ligament, which connects it with the axis. The lateral masses are the most 
bulky and solid parts of the atlas, in order to support the weight of the head. 
Each carries two articular facets, a superior and an inferior. The superior facets 
are of large size, oval, concave, and approach each other in front, but diverge 
behind: they are directed upward, medialward, and a little backward, each forming 
a cup for the corresponding condyle of the occipital bone, and are admirably 
adapted to the nodding movements of the head. Not infrequently they are 



' The costal element of a cervical vertebra not only includes the portion which springs from the side of the body, but 
the anterior and posterior tubercles and the bar of bone which connects them (Fig. 67). 



100 



OSTEOLOGY 



partially subdivided by indentations which encroach upon their margins. The 
inferior articular facets are circular in form, flattened or slightly convex and directed 
downward and medialward, articulating with the axis, and permitting the rotatory 
movements of the head. Just below the medial margin of each superior facet is 
a small tubercle, for the attachment of the transverse atlantal ligament which 
stretches across the ring of the atlas and divides the vertebral foramen into two 
unequal parts — the anterior or smaller receiving the odontoid process of the axis, 
the posterior transmitting the medulla spinalis and its membranes. This part 
of the vertebral canal is of considerable size, much greater than is required for the 
accommodation of the medulla spinalis, and hence lateral displacement of the 
atlas may occur without compression of this structure. The transverse processes 
are large; they project lateralward and downward from the lateral masses, and 
serve for the attachment of muscles which assist in rotating the head. Thev 
are long, and their anterior and posterior tubercles are fused into one mass; the 
foramen transversarium is directed from below, upward and backu^ard. 



Dens 




For alar ligaments 

For trans, ligament of alias 

Superior articular 
surface 



Foramen 

transversarium 



Spinous process 
Fig. 87. — Second cervical vertebra, or epistropheus, from above. 



Second Cervical Vertebra. — The second cervical vertebra (Fig. S7 and SS) is named 
the epistropheus or axis because it forms the pivot upon which the first vertebra, 
carrying the head, rotates. The most distinctive characteristic of this bone is 
the strong odontoid process which rises perpendicularly from the upper surface 
of the body. The body is deeper in front than behind, and prolonged downward 
anteriorly so as to overlap the upper and fore part of the third vertebra. It pre- 
sents in front a median longitudinal ridge, separating two lateral depressions for 
the attachment of the Longus colli muscles. Its under surface is concave from 
before backward and covex from side to side. The dens or odontoid process exhibits 
a slight constriction or neck, where it joins the body. On its anterior surface 
is an oval or nearly circular facet for articulation with that on the anterior arch 
of the atlas. On the back of the neck, and frequenth* extending on to its lateral 
surfaces, is a shallow groove for the transverse atlantal ligament which retains 
the process in position. The apex is pomted, and gi^•es attaclmient to the apical 
odontoid ligament; below the apex the process is somewhat enlarged, and pre- 
sents on either side a rough impression for the attaclmient of the alar ligament; 
these ligaments connect the process to the occipital bone. The internal structure 



THE CERVICAL VERTEBRA 



101 



of the odontoid process is more compact than that of the body. The pedicles 
are broad and strong, espe^cially in front, where they coalesce with the sides of 
the body and the root of the odontoid process. They are covered above by the 
superior articular surfaces. The laminae are thick and strong, and the vertebral 



Odontoid process 



Rough surface for alar ligament 
Groove for transverse atlanial ligament 



Spinous process-^ 




Articular facet for 
anterior arch of atlas 



Body 



Transverse process 
Inferior articular process 

Fig. 88. — Second cervical vertebra, epistropheus, or axis, from the side. 



Transverse 
process 



foramen large, but smaller than that of the atlas. The transverse processes are 
very small, and each ends in a single tubercle; each is perforated by the foramen 
transversarium, which is directed obliquely upward and lateralward. The superior 
articular surfaces are round, slightly convex, directed upward and lateralward, 
and are supported on the body, 

pedicles, and transverse processes. ^"'^'^ 

The inferior articular surfaces have 
the same direction as those of the 
other cervical vertebrae. The supe- 
rior vertebral notches are very shal- 
low, and lie behind the articular 
processes; the inferior lie in front 
of the articular processes, as in the 
other cervical vertebrae. The spinous 
process is large, very strong, deeply 
channelled on its under surface, 
and presents a bifid, tuberculated 
extremity. 

The Seventh Cervical Vertebra 
(Fig. 89). — The most distinctive 
characteristic of this vertebra is 
the existence of a long and promi- 
nent spinous process, hence the 
name vertebra prominens. This pro- 
cess is thick, nearly horizontal in 
direction, not bifurcated, but ter- 
minating in a tubercle to which the lower end of the ligamentum nuchse is 
attached. The transverse processes are of considerable size, their posterior roots 
are large and prominent, while the anterior are small and faintly marked; the 
upper surface of each has usually a shallow sulcus for the eighth spinal nerve, 
and its extremity seldom presents more than a trace of bifurcation. The foramen 




Spinous process 
Fia. 89. — Seventh cervical vertebra. 



102 



OSTEOLOGY 



transversarium may be as large as that in the other cervical vertebrae, but is 
generally smaller on one or both sides; occasionally it is double, sometimes it is 
absent. On the left side it occasionally gives passage to the vertebral artery; 
more frequently the vertebral vein traverses it on both sides; but the usual 
arrangement is for both artery and vein to pass in front of the transverse pro- 
cess, and not through the foramen. wSometimes the anterior root of the trans- 
verse process attains a large size and exists as a separate bone, which is known 
as a cervical rib. 

The Thoracic Vertebrae (Vertebrae Thoracales). 

The thoracic vertebrae (Fig. 90) are intermediate in size between those of 
the cervical and lumbar regions; they increase in size from above downward, the 
upper vertebrae being much smaller than those in the lower part of the region. 
They are distinguished by the presence of facets on the sides of the bodies for 
articulation with the heads of the ribs, and facets on the transverse processes of 
all, except the eleventh and twelfth, for articulation with the tubercles of the ribs. 



Superior articular process 



Demi-facet for head of rib 



Facet for articular part 
of tubercle of rib 




Demi-facet for head of rib 



Inferior articular process 



Fig. 90. — A thoracic vertebra. 



The bodies in the middle of the thoracic region are heart-shaped, and as broad 
in the antero-posterior as in the transverse direction. At the ends of the thoracic 
region they resemble respectively those of the cervical and lumbar vertebrae. 
They are slightly thicker behind than in front, fiat above and below, convex from 
.side to side in front, deeply concave behind, and slightly constricted laterally 
and in front. They present, on either side, two costal demi-facets, one above, 
near the root of the pedicle, the other below, in front of the inferior vertebral 
notch; these are covered with cartilage in the fresh state, and, when the vertebrae 
are articulated with one another, form, with the intervening intervertebral fibro- 
cartilages, oval surfaces for the reception of the heads of the ribs. The pedicles 
are directed backward and slightly upward, and the inferior vertebral notches 
are of large size, and deeper than in any other region of the vertebral column. 
The laminae are broad, thick, and imbricated — that is to say, they overlap those 
of subjacent vertebrae like tiles on a roof. The vertebral foramen is small, and of 
a circular form. The spinous process is long, triangular on coronal section, directed 
obliquely downward, and ends in a tuberculated extremity. These processes 



THE THORACIC VERTEBRA 



103 



overlap from the fifth to the eighth, but are less oblique in direction above and 
below. The superior articular processes are thin plates of bone projecting upward 
from the junctions of the pedicles and lamina; their articular facets are practi- 
cally flat, and are directed backward and a little lateralward and upward. The 
inferior articular processes are fused to a considerable extent with the laminse, 




An entire facet above; 
a datii-facet below 



demi-facet above 



— One entire facet 



One entire facet. 
No facet on trans, proc. 
which is rudimentary 



One entire facet. 

No facet on trans- 
verse process. 
Infer. artic.process 
convex and turned 
lateralwards 



Fio. 91. — Peculiar thoracic vertebrse. 



and project but slightly beyond their lower borders; their facets are directed 
forward and a little medialward and downward. The transverse processes arise 
from the arch behind the superior articular processes and pedicles; they are thick, 
strong, and of considerable length, directed obliquely backward and lateralward, 
and each ends in a clubbed extremity, on the front of which is a small, concave 
surface, for articulation with the tubercle of a rib. 



104 



OSTEOLOGY 



The first, ninth, tenth, eleventh, and twelfth thoracic vertebrae present certain 
pecuHarities, and must be specially considered (Fig. 91). 

The First Thoracic Vertebra has, on either side of the body, an entire articular 
facet for the head of the first rib, and a demi-facet for the upper half of the head 
of the second rib. The body is like that of a cervical vertebra, being broad trans- 
versely; its upper surface is concave, and lipped on either side. The superior 
articular surfaces are directed upward and backward; the spinous process is thick, 
long, and almost horizontal. The transverse processes are long, and the upper 
vertebral notches are deeper than those of the other thoracic vertebrae. 

The Ninth Thoracic Vertebra may have no demi-facets below. In some sub- 
jects however, it has two demi-facets on either side; when this occurs the tenth 
has only demi-facets at the upper part. 

The Tenth Thoracic Vertebra has (except in the cases just mentioned) an entire 
articular facet on either side, which is placed partly on the lateral surface of the 
pedicle. 

In the Eleventh Thoracic Vertebra the body approaches in its form and size 
to that of the lumbar vertebrae. The articular facets for the heads of the ribs 
are of large size, and placed chiefly on the pedicles, which are thicker and stronger 
in this and the next vertebra than in any other part of the thoracic region. The 
spinous process is short, and nearly horizontal in direction. The transverse processes 
are very short, tuberculated at their extremities, and have on articular facets. 

The Twelfth Thoracic Vertebra has the same general characteristics as the 
eleventh, but may be distinguished from it by its inferior articular surfaces being 
convex and directed lateralward, like those of the lumbar vertebrae; by the general 
form of the body, laminae, and spinous process, in which it resembles the lumbar 
vertebrae; and by each transverse process being subdivided into three elevations, 
the superior, inferior, and lateral tubercles: the superior and inferior correspond 
to the mammillary and accessory processes of the lumbar vertebrae. Traces of 
similar elevations are found on the transverse processes of the tenth and eleventh 
thoracic vertebrae. 



Superior articvlar process 




Fig. 92. — A lumbar vertebra seen from the side. 



The Lumbar Vertebrae (Vertebrae Lumbales). 

The lumbar vertebrae (Figs. 92 and 93) are the largest segments of the movable 
part of the vertebral column, and can be distinguished by the absence of a 
foramen in the transverse process, and by the absence of facets on the sides of 
the body. 

The body is large, wider from side to side than from before backward, and a 
little thicker in front than behind. It is flattened or slightly concave above and 



THE LUMBAR VERTEBRA 



105 



below, concave behind, and deeply constricted in front and at the sides. The 
pedicles are very strong, directed backward from the upper part of the body; 



Transverse process 



Inferior articular 

process 



Superior articular 
process 




Mamillary process 
Accessory process 



FiQ. 93. — A lumbar vertebra from above and behind. 



consequently, the inferior vertebral notches are of considerable depth. The 
laminae are broad, short, and strong; the vertebral foramen is triangular, larger 




Fig. 94. — Fifth lumbar vertebra, from above. 



than in the thoracic, but smaller than in the cervical region. The spinous process 
is thick, broad, and somewhat quadrilateral; it projects backward and ends in 



106 OSTEOLOGY 

a rough, uneven border, thickest below where it is occasionally notched. The 
superior and inferior articular processes are well-defined, projecting respectively 
upward and downward from the junctions of pedicles and laminae. The facets 
on the superior processes are concave, and look backward and medialward; those 
on the inferior are convex, and are directed forward and lateralward. The former 
are wider apart than the latter, since in the articulated column the inferior articular 
processes are embraced by the superior processes of the subjacent vertebra. The 
transverse processes are long, slender, and horizontal in the upper three lumbar 
vertebrae; they incline a little upward in the lower two. In the upper three verte- 
brae they arise from the junctions of the pedicles and laminae, but in the lower 
two they are set farther forward and spring from the pedicles and posterior parts 
of the bodies. They are situated in front of the articular processes instead of behind 
them as in the thoracic vertebrae, and are homologous with the ribs. Of the three 
tubercles noticed in connection with the transverse processes of the lower thoracic 
vertebrae, the superior one is connected in the lumbar region with the back part 
of the superior articular process, and is named the mammillary process; the inferior 
is situated at the back part of the base of the transverse process, and is called the 
accessory process (Fig. 93). 

The Fifth Lumbar Vertebra (Fig. 94) is characterized by its body being much 
deeper in front than behind, which accords with the prominence of the sacro- 
vertebral articulation ; by the smaller size of its spinous process ; by the wide interval 
between the inferior articular processes; and by the thickness of its transverse 
processes, which spring from the body as well as from the pedicles. 

The Sacral and Coccygeal Vertebrae. 

The sacral and coccygeal vertebrae consist at an early period of life of nine 
separate segments which are united in the adult, so as to form two bones, five 
entering into the formation of the sacrum, four into that of the coccyx. Some- 
times the coccjTC consists of five bones; occasionally the number is reduced to 
three. 

The Sacrum {os sacrum). — The sacrum is a large, triangular bone, situated 
in the lower part of the vertebral column and at the upper and back part of the 
pelvic cavity, where it is inserted like a wedge between the two hip bones; its 
upper part or base articulates with the last lumbar vertebra, its apex with the 
coccyx. It is curved upon itself and placed very obliquely, its base projecting 
forward and forming the prominent sacrovertebral angle when articulated with 
the last lumbar vertebra; its central part is projected backward, so as to give 
increased capacity to the pelvic cavity. 

Pelvic Surface (fades ijclvina). — The pelvic surface (Fig. 95) is concave from 
above downward, and sHghtly so from side to side. Its middle part is crossed 
by four transverse ridges, the positions of which correspond with the original 
planes of separation between the five segments of the bone. The portions of bone 
intervening between the ridges are the bodies of the sacral vertebrae. The body 
of the first segment is of large size, and in form resembles that of a lumbar vertebra; 
the succeeding ones diminish from above downward, are flattened from before 
backward, and curved so as to accommodate themselves to the form of the sacrum, 
being concave in front, convex behind. At the ends of the ridges are seen the 
anterior sacral foramina, four in number on either side, somewhat rounded in form, 
diminishing in size from above downward, and directed lateralward and forward; 
they give exit to the anterior divisions of the sacral nerves and entrance to the 
lateral sacral arteries. Lateral to these foramina are the lateral parts of the sacrum, 
each consisting of five separate segments at an early period of life; in the adult, 
these are blended with the bodies and with each other. Each lateral part is tra- 



THE SACRAL AND COCCYGEAL VERTEBRA 



107 



versed by four broad, shallow grooves, which lodge the anterior divisions of the 
sacral nerves, and are separated by prominent ridges of bone which give origin 
to the Piriformis muscle. 

If a sagittal section be made through the center of the sacrum (Pig. 99), the 
bodies are seen to be united at their circumferences by bone, wide intervals being 
left centrally, which, in the fresh state, are filled by the intervertebral fibro- 
cartilages. In some bones this union is more complete between the lower than 
the upper segments. 

Dorsal Surface (fades dorsalis) .—The dorsal surface (Fig. 9G) is convex and 
narrower than the pelvic. In the middle line it displays a crest, the middle sacral 
crest, surmounted by three or four tubercles, the rudimentary spinous processes 



Promontory 

\ I 




Fig. 95. — Sacrum, pelvic surface. 



of the upper three or four sacral vertebrae. On either side of the middle sacral 
crest is a shallow groove, the sacral groove, which gives origin to the iNIultifidus, 
the floor of the groove being formed by the united laminae of the corresponding 
vertebrae. The laminae of the fifth sacral vertebra, and sometimes those of the 
fourth, fail to meet behind, and thus a hiatus or deficiency occurs in the posterior 
wall of the sacral canal. On the lateral aspect of the sacral groove is a linear 
series of tubercles produced by the fusion of the articular processes which together 
form the indistinct sacral articular crests. The articular processes of the first 
sacral vertebra are large and oval in shape; their facets are concave from side to 
side, look backward and medialward, and articulate with the facets on the inferior 
processes of the fifth lumbar vertebra. The tubercles which represent the inferior 
articular processes of the fifth sacral vertebra are prolonged downward as rounded 



108 



OSTEOLOGY 



processes, which are named the sacral comua, and are connected to the cornua 
of the coccyx. Lateral to the articular processes are the four posterior sacral 
foramina; they are smaller in size and less regular in form than the anterior, and 
transmit the posterior divisions of the sacral nerves. On the lateral side of the 
posterior sacral foramina is a series of tubercles, which represent the transverse 
processes of the sacral vertebrae,, and form the lateral crests of the sacrum. The 
transverse tubercles of the first sacral vertebra are large and very distinct; they, 
together with the transverse tubercles of the second vertebra, give attacliment 
to the horizontal parts of the posterior sacroiliac ligaments; those of the third 
vertebra give attaclmient to the oblique fasciculi of the posterior sacroiliac liga- 
ments; and those of the fourth and fifth to the sacrotuberous ligaments. 




Sacrospinal 



— Latissimus 
dor si 



Sacrospinalts 



Upper half of fifth 

rior sacral foramen 



Fig. 96. — Sacrum, dorsal surface. 



Lateral Surface. — The lateral surface is broad above, but narrowed into a thin 
edge below. The upper half presents in front an ear-shaped surface, the auricular 
surface, covered with cartilage in the fresh state, for articulation with the ilium. 
Behind it is a rough surface, the sacral tuberosity, on which are three deep 
and uneven impressions, for the attachment of the posterior sacroiliac ligament. 
The lower half is thin, and ends in a projection called the inferior lateral angle; 
medial to this angle is a notch, which is converted into a foramen by the trans- 
verse process of the first piece of the cocc\'x, and transmits the anterior division of 
the fifth sacral nerve. The thin lower half of the lateral surface gives attachment 
to the sacrotuberous and sacrospinous ligaments, to some fibers of the Gluteeus 
maximus behind, and to the Coccygeus in front. 

Base Q)asis oss. sacri). — The base of the sacrum, which is broad and expanded, 
is directed upward and forward. In the middle is a large oval articular surface, 



THE SACRAL AND COCCYGEAL VERTEBRA 



109 



the upper surface of the body of the first sacral vertebra, which is connected with 
the under surface of the body of the last lumbar vertebra by an intervertebral 



Articular process 
Medial sacral crest 




Cornu of sacrum^ 

Cornu of coccyx 



Fig. 97. — Lateral surfaces of sacrum and coccyx. 



Sacral canal 

Articular process 




Fig. 98 — Base of sacrum. 



no 



OSTEOLOGY 



fibrocartilage. Behind this is the large triangular orifice of the sacral canal, which 
is completed by the laminse and spinous process of the first sacral vertebra. The 
superior articular processes project from it on either side; they are oval, concave, 
directed backward and medialward, like the superior articular processes of a lumbar 
vertebra. They are attached to the body of the first sacral vertebra and to the 
alse by short thick pedicles; on the upper surface of each pedicle is a vertebral 
notch, which forms the lower part of the foramen between the last lumbar and first 
sacral vertebrae. On either side of the body is a large triangular surface, which 
supports the Psoas major and the lumbosacral trunk, and in the articulated 
pelvis is continuous with the iliac fossa. This is called the ala; it is slightly concave 




Cornua 




Anterior Surface 



Rudim. 
Trans, 
prac. 




Posterior surface 



FlQ. 99. — Median sagittal section of the sacrum. 



Fig. 100.— Coccyx. 



from side to side, convex from before backward, and gives attachment to a few 
of the fibers of the Iliacus. The posterior fourth of the ala represents the trans- 
verse process, and its anterior three-fourths the costal process of the first sacral 
segment. 

Apex (apex oss. sacri). — ^The apex is directed downward, and presents an oval 
facet for articulation with the coccyx. 

Vertebral Canal (canalis sacralis; sacral canal). — The vertebral canal (Fig. 99) 
runs throughout the greater part of the bone; above, it is triangular in form; 
below, its posterior wall is incomplete, from the non-development of the laminse 
and spinous processes. It lodges the sacral nerves, and its walls are perforated by 
the anterior and po-sterior sacral foramina through which these nerves pass out. 



THE SACRAL AND COCCYGEAL VERTEBRA 111 

Structure. — The sacrum consists of cancellous tissue enveloped by a thin layer of compact bone. 

Articulations. — The sacrum articulates with four bones; the last lumbar vertebra above, the 
coccyx below, and the hip bone on either side. 

Differences in the Sacrum of the Male and Female. — In the female the sacrum is shorter and 
wider than in the male; the lower half forms a greater angle with the upper; the upper half is 
nearly straight, the lower half presenting the greatest amount of curvature. The bone is also 
directed more obliquely backward; this increases the size of the pelvic cavity and renders the 
sacrovertebral angle more prominent. In the male the curvature is more evenly distributed 
over the whole length of the bone, and is altogether greater than in the female. 

Variations. — The sacrum, in some cases, consists of six pieces; occasionally the number is 
reduced to four. The bodies of the first and second vertebrae may fail to unite. Sometimes 
the uppermost transverse tubercles are not joined to the rest of the ala on one or both sides, 
or the sacral canal may be open throughout a considerable part of its length, in consequence of 
the imperfect development of the laminae and spinous processes. The sacrum, also, varies con- 
siderably with respect to its degree of curvature. 

The Coccyx (os coccygis). — The coccyx (Fig. 100) is usually formed of four 
rudimentary vertebrae; the number may however be increased to five or diminished 
to three. In each of the first three segments may be traced a rudimentary body 
and articular and transverse processes; the last piece (sometimes the third) is a 
mere nodule of bone. All the segments are destitute of pedicles, laminae, and 
spinous processes. The first is the largest; it resembles the lowest sacral vertebra, 
and often exists as a separate piece; the last three diminish in size from above 
downward, and are usually fused with one another. 

Surfaces. — The anterior surface is slightly concave, and marked with three trans- 
verse grooves which indicate the junctions of the different segments. It gives 
attachment to the anterior sacrococcygeal ligament and the Levatores ani, and 
supports part of the rectum. The posterior surface is convex, marked by transverse 
grooves similar to those on the anterior surface, and preseiits on either side a linear 
row of tubercles, the rudimentary articular processes of the coccygeal vertebrae. 
Of these, the superior pair are large, and are called the coccygeal comua; they 
project upward, and articulate with the cornua of the sacrum, and on either side 
complete the foramen for the transmission of the posterior division of the fifth 
sacral nerve. 

Borders. — The lateral borders are thin, and exhibit a series of small eminences, 
which represent the transverse processes of the coccygeal vertebrae. Of these, 
the first is the largest; it is flattened from before backward, and often ascends 
to join the lower part of the thin lateral edge of the sacrum, thus completing the 
foramen for the transmission of the anterior division of the fifth sacral nerve; 
the others diminish in size from above downward, and are often wanting. The 
borders of the coccyx are narrow, and give attachment on either side to the sacro- 
tuberous and sacrospinous ligaments, to the Coccygeus in front of the ligaments, 
and to the Glutaeus maximus behind them. 

Base. — The base presents an oval surface for articulation with the sacrum. 

Apex. — The apex is rounded, and has attached to it the tendon of the Sphincter 
ani externus. It may be bifid, and is sometimes deflected to one or other side. 

Ossification of the Vertebral Colimm. — Each cartilaginous vertebra is ossified from three primary 
centers (Fig. 101), two for the vertebral arch and one for the body.' Ossification of the vertebral 
arches begins in the upper cervical vertebrae about the seventh or eighth week of fetal hfe, and grad- 
ually extends down the column. The ossific granules first appear in the situations where the trans- 
verse processes afterward project, and spread backward to the spinous process forward into the 
pedicles, and lateralward into the transverse and articular processes. Ossification of thebodies begins 
about the eighth week in the lower thoracic region, and subsequently extends upward and down- 
ward along the column. The center for the body does not give rise to the whole of the body of 
the adult vertebra, the postero-lateral portions of which are ossified by extensions from the verte- 
bral arch centers. The body of the vertebra during the first few years of life shows, therefore, 

■ A vertebra is occasionally found in which the body consists of two lateral portions — a condition which proves that 
the body is sometimes ossified from two primary centers, one on either side of the middle line. 



112 



OSTEOLOGY 



two sjTichondroses, neurocentral synchondroses, traversing it along the planes of junction of 
the three centers (Fig. 102). In the thoracic region, the facets for the heads of the ribs lie behind 

the neurocentral synchondroses and 
Fig. 101. — Ossification of a vertebra 
By 3 primary centers 

1 for body (Slh week) 



are ossified from the centers for the 
vertebral arch. At birth the vertebra 
consists of three pieces, the body and 
the halves of the vertebral arch. Dur- 
ing the first year the halves of the 
arch unite behind, union taking place 
first in the lumbar region and then 
extending upward through the thoracic 
and cervical regions. About the third 
year the bodies of the upper cervical 
vertebrae are joined to the arches on 
either side; in the lower lumbar verte- 
brae the union is not completed until the 
sixth year. Before puberty, no other 




Ijor each vertebral arch {lih or 8<A week) 

Fig. 102. 
By 3 secondary centers 



Neurocentral 
synchondrosis 




1 for each 
trans, process 
\Qth year 



1 for spinous process ( IQth year) 

Fig. 103. 
By 2 additional plates 

1 for upper surface^ 
of body 




. ].6th year 



1 for under surface 
of body 



Fig. 104.— Atlas. 



By .3 centers 




1 for anter. arch {end cf 1st year) 

I for each \m week 

lateral mass j 

Fig. 105.— Axis. 



By 7 centers 



2nd year 




Gth month 
1 /or each vertebral arch (i 

or Sth iteek) 
1 for body {4th month) 
1 /or under sur/ace o/body 



th 



Fig. 106. — Lumbar vertebra. 




2 additional centers for mammillary processes 






Additional centers 
for costal elements* 



At birth 




Fig. 107 



At 4^ yrs 




Fig. 108 



Two epiphysial plates 
for each lateral surface * 



At 
25th year 




Fig. 107-109. — Ossification of the sacrum. 



changes occur, excepting a gradual increase of these primary centers, the upper and under sur- 
faces of the bodies and the ends of the transverse and spinous processes bemg cartilagmous. 



THE SACRAL AND COCCYGEAL VERTEBRA 



113 



About the sixteenth year (Fig. 102), five secondary centers appear, one for the tip of each transverse 
process, one for the extremity of the spinous process, one for the upper and one for the lower 
surface of the body (Fig. 103). These fuse with the rest of the bone about the age of twenty-five 
Exceptions to this mode of development occur in the first, second, and seventh cervical verte- 
brae, and in the lumbar vertebrae. 

Atlas.— The atlas is usually ossified from three centers (Fig. 104). Of these, one appears in 
each lateral mass about the seventh week of fetal life, and extends backward; at birth, these 
portions of bone are separated from one another behind by a narrow interval filled with cartilage 
Between the third and fourth years they unite either directly or through the medium of a separate 
center developed in the cartilage. At birth, the anterior arch consists of cartilage; in this a 
separate center appears about the end of the first year after birth, and joins the lateral masses 
from the sixth to the eighth year— the lines of union extending across the anterior portions of 
the superior articular facets. OccasionaUy there is no separate center, the anterior arch being 
formed by the forward extension and ultimate junction of the two lateral masses; sometimes 
this arch is ossified from two centers, one on either side of the middle line. 

Epistropheus or Axis.— The axis is ossified from five primary and two secondary centers (Fig. 
105). The body and vertebral arch are ossified in the same manner as the corresponding parts 
in the other vertebrae, viz., one center for the body, and two for the vertebral arch. The centers 
for the arch appear about the seventh or eighth week of fetal fife, that for the body about the 
fc irth or fifth month. The dens or odontoid process consists originally of a continuation upward 
of the cartilaginous mass, in which the lower part of the body is formed. About the sixth month 
of fetal life, two centers make their appearance in the base of this process: they are placed 
laterally, and join before birth to form a conical bilobed mass deeply cleft above; the interval 
between the sides of the cleft and the summit of the process is formed by a wedge-shaped piece 
of cartilage. The base of the process is separated from the body by a cartilaginous disk, which 
gradually becomes ossified at its circumference, but remains cartilaginous in its center until 
advanced age. In this cartilage, rudiments of the lower epiphysial lamella of the atlas and 
the upper epiphysial lamella of the axis may sometimes be found. The apex of the odontoid 
process has a separate center which appears in the second and joins about the twelfth year; this 
is the upper epiphysial lamella of the atlas. In addition to these there is a secondary center for 
a thin epiphysial plate on the under surface of the body of the bone. 

The Seventh Cervical Vertebra.— The anterior or costal part of the transverse process of this 
vertebra is sometimes ossified from a separate center which appears about the sixth month of 
fetal life, and joins the body and posterior part of the transverse process between the fifth and 
sixth years. Occasionally the costal part persists as a separate piece, and, becoming lengthened 
lateralward and forward, constitutes what is known as a cervical rib. Separate ossific centers 
have also been found in the costal processes of the fourth, fifth, and sixth cervical vertebrae. 

Lumbar Vertebrae.- The lumbar vertebrae (Fig. 106) have each two additional centers, for 
the mammillary processes. The transverse process of the first lumbar is sometimes developed as 
a separate piece, which may remain permanently ununited with the rest of the bone, thus form- 
ing a lumbar rib — a peculiarity, however, 
rarely met with. 

Sacrum (Figs. 107 to 110).— The body 
of each sacral vertebra is ossified from a 
primary center and two epiphysial plates, 
one for its upper and another for its under 
surface, while each vertebral arch is ossi- 
fied from two centers. 

The anterior portions of the lateral parts 
have six additional centers, two for each 
of the first three vertebrae; these represent 
the costal elements, and make their ap- 
pearance above and lateral to the anterior 
sacral foramina (Figs. 107, 108). 

On each lateral surface two epiphysial plates are developed (Figs. 109, 1 10) : one for the auric- 
ular surface, and another for the remaining part of the thin lateral edge of the bone.i 

Periods of Ossification. — About the eighth or ninth week of fetal Ufe, ossification of the 
central part of the body of the first sacral vertebra commences, and is rapidly followed by deposit 
of ossific matter in the second and third; ossification does not commence in the bodies of the 
lower two segments until between the fifth and eighth months of fetal life. Between the sixth 



Center for 
neural a 



Center for 
neural arch. 



Costal 
dement 




Costal 
element. 



body. 



Lateral 
epiphysis. 

Fig. 110. — Base of young sacrum 



Lateral 
epiphysis. 



' The ends of the spinous processes of the upper three sacral vertebrae are sometimes developed from separate 
epiphyses, and Fawcett (Anatomischer Anzeiger, 1907, Band xxx) states that a number of epiphysial nodules may be 
seen in the sacrum at the age of eighteen years. These are distributed as follows: One for each of the mammillary pro- 
cesses of the first sacral vertebra ; twelve — six on either side — in connection with the costal elements (two each for the first 
and second and one each for the third and fourth) and eight for the transverse processes — four on either side — one each 
for the first, third, fourth, and fifth. He is further of opinion that the lower part of each lateral surface of the sacrum 
is formed by the extension and union of the third and fourth "costal" and fourth and fifth "transverse" epiphyses. 



114 OSTEOLOGY 

and eighth months ossification of the vertebral arches takes place; and about the same time the 
costal centers for the lateral parts make their appearance. The junctions of the vertebral 
arches with the bodies take place in the lower vertebrae as early as the second year, Lut are not 
effected in the uppermost until the fifth or sixth year. About the sixteenth year the epiphysial 
plates for the upper and under surfaces of the bodies are formed; and between the eighteenth and 
twentieth years, those for the lateral surfaces make their appearance. The bodies of the sacral 
vertebrae are, during early hfe, separated from each other by intervertebral fibrocartilages, but 
about the eighteenth year the two lowest segments become united by bone, and the process of 
bony union gradually extends upward, with the result that between the twenty-fifth and thirtieth 
j^ears of hfe all the segments are united. On examining a sagittal section of the sacrum, the situa- 
tions of the intervertebral fibrocartilages are indicated by a series of oval cavities (Fig. 99). 

Coccyx. — The coccyx is ossified from four centers, one for each segment. The ossific nuclei 
make their appearance in the following order: in the first segment between the first and fourth 
years; in the second between the fifth and tenth years; in the third between the tenth and fifteenth 
years; in the fourth between the fourteenth and twentieth years. As age advances, the segments 
unite with one another, the union between the first and second segments being frequently delaj^ed 
until after the age of twenty-five or thirty. At a late period of life, especially in females, the coccyx 
often fuses with the sacrum. 

THE VERTEBRAL COLUMN AS A WHOLE. 

The vertebral column is situated in the median line, as the posterior part of the 
trunk; its average length in the male is about 71 cm. Of this length the cervical 
part measures 12.5 cm., the thoracic about 28 cm., the lumbar 18 cm., and the 
sacrum and qoqqxx 12.5 cm. The female column is about 61 cm. in length. 

Curves. — ^\'iewed laterally (Fig. Ill), the vertebral column presents several 
curves, which correspond to the different regions of the column, and are called 
cervical, thoracic, lumbar, and pelvic. The cervical curve, convex forward, begins 
at the apex of the odontoid process, and ends at the middle of the second thoracic 
vertebra; it is the least marked of all the curves. The thoracic curve, concave for- 
ward, begins at the middle of the second and ends at the middle of the twelfth 
thoracic vertebra. Its most prominent point behind corresponds to the spinous 
process of the seventh thoracic vertebra. The lumbar curve is more marked in 
the female than in the male; it begins at the middle of the last thoracic vertebra, 
and ends at the sacrovertebral angle. It is convex anteriorly, the convexity of 
the lower three vertebrae being much greater than that of the upper two. The 
pelvic curve begins at the sacrovertebral articulation, and ends at the point of the 
coccyx; its concavity is directed downward and forward. The thoracic and pelvic 
curves are termed primary curves, because they alone are present during fetal life. 
The cervical and lumbar curves are compensatory or secondary, and are developed 
after birth, the former when the child is able to hold up its head (at three or four 
months), and to sit upright (at nine months), the latter at twelve or eighteen 
months, when the child begins to walk. 

The vertebral column has also a slight lateral curvature, the convexity of which 
is directed toward the right side. This may be produced by muscular action, 
most persons using the right arm in preference to the left, especially in making 
long-continued efforts, when the body is curved to the right side. In support of 
this explanation it has been found that in one or two individuals who were left- 
handed, the convexity was to the left side. By others this curvature is regarded as 
being produced by the aortic arch and upper part of the descending thoracic 
aorta — a view which is supported by the fact that in cases where the viscera are 
transposed and the aorta is on the right side, the convexity of the curve is 
directed to the left side. 

Surfaces. — Anterior Surface. — When viewed from in front, the width of the bodies 
of the vertebrse is seen to increase from the second cervical to the first thoracic; 
there is then a slight diminution in the next three vertebrse; below this there 
is again a gradual and progressive increase in width as low as the sacrovertebral 
angle. From this point there is a rapid diminution, to the apex of the coccyx. 



THE VERTEBRAL COLUMN AS A WHOLE 



115 



Posterior Surface. — The posterior surface 
of the vertebral cohimn presents in the 
median Hne the spinous processes. In the 
cervical region (with the exception of the 
second and seventh vertebrae) these are 
short and horizontal, with bifid extremities. 
In the upper part of the thoracic region 
they are directed obliquely downward; in 
the middle they are almost vertical, and in 
the lower part they are nearly horizontal. 
In the lumbar region they are nearly hori- 
zontal. The spinous processes are separated 
by considerable intervals in the lumbar 
region, by narrower intervals in the neck, 
and are closely approximated in the middle 
of the thoracic region. Occasionally one of 
these processes deviates a little from the 
median line — a fact to be remembered in 
practice, as irregularities of this sort are 
attendant also on fractures or displacements 
of the vertebral column. On either side of 
the spinous processes is the vertebral groove 
formed by the laminae in the cervical and 
lumbar regions, where it is shallow, and by 
the laminae and transverse processes in the 
thoracic region, wdiere it is deep and broad ; 
these grooves lodge the deep muscles of the 
back. Lateral to the vertebral grooves are 
the articular processes, and still more later- 
ally the transverse processes. In the tho- 
racic region, the transverse processes stand 
backward, on a plane considerably behind 
that of the same processes in the cervical 
and lumbar regions. In the cervical region, 
the transverse processes are placed in front 
of the articular processes, lateral to the 
pedicles and between the intervertebral 
foramina. In the thoracic region they are 
posterior to the pedicles, intervertebral 
foramina, and articular processes. In the 
lumbar region they are in front of the 
articular processes, but behind the inter- 
vertebral foramina. 

Lateral Surfaces. — The lateral surfaces are 
separated from the posterior surface by the 
articular processes in the cervical and lum- 
bar regions, and by the transverse processes 
in the thoracic region. They present, in 
front, the sides of the bodies of the verte- 
brae, marked in the thoracic region by the 
facets for articulation with the heads of 
the ribs. More posteriorly are the inter- 
vertebral foramina, formed by the juxta- 
position of the vertebral notches, oval in 



Jst cervical 
or Atlas 

2nd cervical 
or Axis 



W\ 



1st thoracic-\ 



2-\ 



4' 



*-l 



9-} f 



:>H^' 



io-l 



ii~ 



)i^m- 



■ If'S 



«'U 



tl 



1^ 



1st lumbar - 



'""i«ii^ 



>.: 



.*^i 






Fia. 111. — Lateral view of the vertebral column. 



116 



OSTEOLOGY 



shape, smallest in the cervical and upper part of the thoracic regions, and gradually 
increasing in size to the last lumbar. They transmit the spinal nerves and are 
situated between the transverse processes in the cervical region, and in front of 
them in the thoracic and lumbar regions. 

Vertebral Canal. — The vertebral canal follows the different curves of the column; 
it is large and triangular in those parts of the column which enjoy the greatest 
freedom of movement, viz., the cervical and lumbar regions; and is small and 
rounded in the thoracic region, where motion is more limited. 

Abnormalities. — Occasionally the coalescence of the laminae is not completed, and conse- 
quently a cleft is left in the arches of the vertebra), through which a protrusion of the spinal 
membranes (dura mater and arachnoid), and generally of the medulla spinahs itself, takes place, 
constituting the malformation known as spina bifida. This condition is most common in the 
lumbosacral region, but it may occur in the thoracic or cervical region, or the arches throughout 
the whole length of the canal may remain incomplete. 



-First thoracic 




Fig. 112. — The thorax from in front. (Spalteholz.) 

THE THORAX. 

The skeleton of the thorax or chest (Figs. 112, 113, 114) is an osseo-cartilaginous 
cage, containing and protecting the principal organs of respiration and circulation. 



THE THORAX 



117 



It IS conical in shape, being narrow above and broad below, flattened from before 
backward, and longer behind than in front. It is somewhat reniform on trans- 
verse section on account of the projection of the vertebral bodies into the cavitv 



First thoracic 




Fig. 113 — The thorax from behind. (Spalteholz.) 



Boundaries. — The posterior surface is formed by the twelve thoracic vertebrae 
and the posterior parts of the ribs. It is convex from above downward, and pre- 
sents on either side of the middle line a deep groove, in consequence of the lateral 
and backward direction which the ribs take from their vertebral extremities to 
their angles. The anterior surface, formed by the sternum and costal cartilages, 
is flattened or slightly convex, and inclined from above downward and forward. 
The lateral surfaces are convex; they are formed by the ribs, separated from 
each other by the intercostal spaces, eleven in number, which are occupied by 
the Intercostal muscles and membranes. 

The upper opening of the thorax is veniform in shape, being broader from side 
to side than from before backward. It is formed by tlie first thoracic vertebra 
behind, the upper margin of the sternum in front, and the first rib on either side. 



118 



OSTEOLOGY 



It slopes downward and forward, so that the anterior part of the opening is on a 
lower level than the posterior. Its antero-posterior diameter is about 5 cm., and 
its transverse diameter about 10 cm. The lower opening is formed by the twelfth 
thoracic vertebra behmd, by the eleventh and twelfth ribs at the sides, and in front 
by the cartilages of the tenth, ninth, eighth, and seventh ribs, which ascend on 
either side and form an angle, the subcostal angle, into the apex of which the 



sternum 



Twelfth thoracic 



First lumbar 




Fig. 114 — The thorax from the right. (Spalteholz.) 



xiphoid process projects. The lower opening is wider transversely than from 
before backward, and slopes obliquely downward and backward, it is closed by 
the diaphragm which forms the floor of the thorax. 



The thorax of the female differs from that of the male as follows: 1. Its capacity is less. 2. 
The sternum is shorter. 3. The upper margin of the sternum is on a level with the lower part 
of the body of the third thoracic vertebra, whereas in the male it is on a level with the lower 
part of the body of the second. 4. The upper ribs are more movable, and so allow a greater 
enlargement of the upper part of the thorax. 



THE STERNUM 



119 



The Sternum (Breast Bone). 

The sternum (Figs. 115 to 117) is an elongated, flattened bone, forming the 
middle portion^ of the anterior wall of the thorax. Its upper end supports the 
clavicles, and its margins articulate with the cartilages of the first seven pairs 

STERNOCUEIDOMASTOIDEUS 
SUBCLAVICS "\ '^'fffulaf 




Fig. 115. — Anterior surface of sternum and costa cartilages. 



of ribs. It consists of three parts, named from above downward, the manubrium, 
the body or gladiolus, and the xiphoid process; in early life the body consists of four 
segments or sterncbrce. In its natural position the inclination of the bone is oblique 
from above, downward and forward. It is slightly convex in front and concave 



120 



OSTEOLOGY 



behind; broad above, becoming narrowed at the point where the manubrium joins 
the body, after which it again widens a little to below the middle of the body, 
and then narrows to its lower extremity. Its average length in the adult is about 
17 cm., and is rather greater in the male than in the female. 

Manubrium (manubrium sterni). — The manubrium is of a somewhat quad- 
rangular form, broad and thick abo^'e, narrow below at its junction with the body. 

Surfaces. — Its anterior surface, convex from side to side, concave from above 
downward, is smooth, and affords attachment on either side to the sternal 
origins of the Pectoralis major and Sternocleidomastoideus. Sometimes the 
ridges limiting the attachments of these muscles are very distinct. Its posterior 
surface, concave and smooth, affords attachment on either side to the Sterno- 
hyoideus and Sternothyreoideus. 




For 1st 
- custal 
canilage 



Sternal 
angle 



Xiphoid procesf 



FiQ. 116. — Posterior surface of sternum. 




Articular surface 
for clavicle 

Depression for 

Idit costal cartilage 

Manvbrium 

Demifacets for 2nd costal 
cartilage 



Facet fpf Zrd costal cartilage 
Body 



Facet for Alh costal cartilage 

Facet for 5th costal cartilage 

- Facet for Gth costal cartilage 
Facet for 7th costal cartilage 

Xiphoid process 



Fig. 117. — Lateral border of sternum. 



Borders. — The superior border is the thickest and presents at its center the jugular 
or prestemal notch; on either side of the notch is an oval articular surface, directed 
upward, backward, and lateralward, for articulation with the sternal end of the 
clavicle. The inferior border, oval and rough, is covered in a fresh state with a 
thin layer of cartilage, for articulation with the body. The lateral borders are each 
marked above by a depression for the first costal cartilage, and below by a small 
facet, which, with a similar facet on the upper angle of the body, forms a notch 
for the reception of the costal cartilage of the second rib. Between the depression 
for the first costal cartilage and the demi-facet for the second is a narrow, curved 
edge, ^\•hich slopes from above downward and medialward. 

Body (corpus sterni; gladiolus). — The body, considerably longer, narrower, and 
thinner than the manubrium, attains its greatest breadth close to the lower end. 

Surfaces. — Its anterior surface is nearly fiat, directed upward and forward, 
and marked by three transverse ridges which cross the bone opposite the third. 



THE STERNUM 121 

fourth, and fifth articuhir depressions.^ It affords attachment on either side to 
the sternal origin of the PectoraHs major. At the junction of the third and fourth 
pieces of the body is occasionally seen an orifice, the sternal foramen, of var^•ing 
size and form. The posterior surface, slightly concave, is also marked by three 
transverse lines, less distinct, however, than those in front; from its lower part, 
on either side, the Transversus thoracis takes origin. 

Borders.— The superior border is oval and articulates with the manubrium, the 
junction of the two forming the sternal angle (anguhis Liidovici^). The inferior 
border is narrow, and articulates with the xiphoid process. Each lateral border 
(Fig. 117), at its superior angle, has a small facet, which with a similar facet on 
the manubrium, forms a cavity for the cartilage of the second rib; below this 
are four angular depressions which receive the cartilages of the third, fourth, 
fifth, and sixth ribs, while the inferior angle has a small facet, which, with a cor- 
responding one on the xiphoid process, forms a notch for the cartilage of the seventh 
rib. These articular depressions are separated by a series of curved interarticular 
intervals, which diminish in length from above downward, and correspond to 
the intercostal spaces. Most of the cartilages belonging to the true ribs, as will 
be seen from the foregoing description, articulate with the sternum at the lines 
of junction of its primitive component segments. This is well seen in many of 
the lower animals, where the parts of the bone remain ununited longer than in 
man. 

Xiphoid Process (processus xipJwideus; ensiform or xiphoid appendix). — The 
xiphoid process is the smallest of the three pieces: it is thin and elongated, 
cartilaginous in structure in youth, but more or less ossified at its upper part in 
the adult. 

Surfaces. — Its anterior surface affords attachment on either side to the anterior 
costoxiphoid ligament and a small part of the Rectus abdominis; its posterior sur- 
face, to the posterior costoxiphoid ligament and to some of the fibers of the dia- 
phragm and Transversus thoracis, its lateral borders, to the aponeuroses of the 
abdominal muscles. Above, it articulates wdth the lower end of the body, and 
on the front of each superior angle presents a facet for part of the cartilage of the 
seventh rib; below, by its pointed extremity, it gives attachment to the Imea 
alba. The xiphoid process varies much in form; it may be broad and thin, pointed, 
bifid, perforated, curved, or deflected considerably to one or other side. 

Structure.^The sternum is composed of highly vascular cancellous tissue, covered by a thin 
layer of compact bone which is thickest in the manubrium between the articular facets for the 
clavicles. 

Ossification. — The sternum originally consists of two cartilaginous bars, situated one on either 
side of the median plane and connected with the cartilages of the upper nine ribs of its own side. 
These two bars fuse with each other along the middle line to form the cartilaginous sternum which 
is ossified from six centers: one for the manubrium, four for the body, and one for the xiphoid 
process (Fig. IIS). The ossific centers appear in the intervals between the articular depressions 
for the costal cartilages, in the following order; in the manubrium and first piece of the body, 
during the sixth month ; in the second and third pieces of the body, during the seventh month of 
fetal life; in its fourth piece, during the first year after birth; and in the xiphoid process, between 
the fifth and eighteenth years. The centers make their appearance at the upper parts of the seg- 
ments, and proceed gradually downward.^ To these may be added the occasional existence of 
two small episternal centers, which make their appearance one on either side of the jugular notch; 
they are probably vestiges of the episternal bone of the monotremata and lizards. Occasionally 
some of the segments are formed from more than one center, the number and position of which 
vary (Fig. 120). Thus, the first piece may have two, three, or even six centers. When two are 

1 Paterson (The Human Sternum, 1904), who examined 521 specimens, points out that these ridges are altogether 
absent in 26.7 per cent. ; that in 09 per cent, a ridge exists opposite the third co.-itiil attachment; in 39 per cent, opposite 
the fourth; and in 4 per cent, only, opposite the fifth. 

2 Named after the French surgeon Antoine Louis, 1723-1792. The Latin name angulus Ludovici is not infrequently 
mistranslated into English as " the angle of Ludwig. " 

^ Out of 141 sterna between the time of birth and the age of sixteen years, Paterson {.op. cit.) found the fourth or 
lowest center for the body present only in thirty-eight cases — i. e., 26.9 per cent. 



122 



OSTEOLOGY 



Time 

of 
appearance 



Time 

of 
union 



In 

number of 
centers 



In 

mode of 
union 




1 for manvhrium 



^6th month 



4 for body 



5 1st year after birth 



7th month 



I „ , 1 for xiphoid \ 

!»' process j5th to 18th year 

Fig. lis. — Ossification of the sternum. 




Rarely unite, except in old age 
Between puberty and the 25th year 




Partly cartilaginous to advanced life 
Fig. 119 

for first piece, two or more centers 

for second piece, usually one 

for third \ 

(2, placed laterally 
for fourth J 

for fifth 



Fig. 120. — Peculiarities. 




Arrest of ossification of lateral pieces, 
produciiig : 

Sternal fissure, and 



Sternul foramen 



Fig. 121 



THE RIBS 123 

present, they are generally situated one above the other, the upper being the larger; the second 
piece has seldom more than one; the third, fourth, and fifth pieces are often formed from two 
centers placed laterally, the irregular union of which explains the rare occurrence of the sternal 
foramen (Fig. 121), or of the vertical fissure which occasionally intersects this part of the bone 
constituting the malformation known as fissura sterni; these conditions are further explained by 
the manner in which the cartilaginous sternum is formed. More rarely still the upper end of the 
sternum may be divided by a fissure. Union of the various centers of the body begins about 
puberty, and proceeds from below upward (Fig. 119) ; by the age of twenty-five they are all united. 
The xiphoid process may become joined to the body before the age of thirty, but this occurs 
more frequently after forty; on the other hand, it sometimes remains ununited in old age. In 
advanced life the manubrium is occasionally joined to the body by bone. When this takes place, 
however, the bony tissue is generally only superficial, the central portion of the intervening 
cartilage remaining unossified. 

Articulations. — The sternum articulates on either side with the clavicle and upper seven costal 
cartilages. 

The Ribs (Costse). 

The ribs are elastic arches of bone, which form a large part of the thoracic 
skeleton. They are twelve in number on either side; but this number mav be 
increased by the development of a cervical or lumbar rib, or may be diminished 
to eleven. The first seven are connected behind with the vertebral column, and in 
front, through the intervention of the costal cartilages, with the sternum (Fig. 
115); they are called true or vertebro-stemal ribs.^ The remaining five are false 
ribs; of these, the first three have their cartilages attached to the cartilage of the 
rib above (vertebro-chondral) : the last two are free at their anterior extremities 
and are termed floating or vertebral ribs. The ribs vary in their direction, the 
upper ones being less oblique than the lower; the obliquity reaches its maximum 
at the ninth rib, and gradually decreases from that rib to the twelfth. The ribs 
are situated one below the other in such a manner that spaces called intercostal 
spaces are left between them. The length of each space corresponds to that of 
the adjacent ribs and their cartilages; the breadth is greater in front than behind, 
and between the upper than the lower ribs. The ribs increase in length from 
the first to the seventh, below which thev diminish to the twelfth. In breadth 
they decrease from above downward; in the upper ten the greatest breadth is at 
the sternal extremity. 

Common Characteristics of the Ribs (Figs. 122, 123). — A rib from the middle 
of the series should be taken in order to study the common characteristics of these 
bones. 

Each rib has two extremities, a posterior or vertebral, and an anterior or sternal, 
and an intervening portion — the body or shaft. 

Posterior Extremity. — The posterior or vertebral extremity presents for examination 
a head, neck, and tubercle. 

The head is marked by a kidney-shaped articular surface, divided by a hori- 
zontal crest into two facets for articulation with the depression formed on the 
bodies of two adjacent thoracic vertebrae; the upper facet is the smaller; to the 
crest is attached the interarticular ligament. 

The neck is the flattened portion which extends lateralward from the head; it 
is about 2.5 cm. long, and is placed in front of the transverse process of the 
lower of the two vertebrse with which the head articulates. Its anterior surface is 
flat and smooth, its posterior rough for the attachment of the ligament of the neck, 
and perforated by numerous foramina. Of its two borders the superior presents a 
rough crest {crista colli costxp) for the attachment of the anterior costotransverse 
ligament; its inferior border is rounded. On the posterior surface at the junction 
of the neck and body, and nearer the lower than the upper border, is an eminence 

' Sometimes the eighth rib cartilage articulates with the sternum; this condition occurs more frequently on the 
right than on the left side. 



124 



OSTEOLOGY 



—the tubercle ; it consists of an articular and a non-articular portion. The articular 
portion, the lower and more medial of the two, presents a small, oval surface for 



Angle 



Non-articular part 0/ tubercle 

Articular part of tubercle 



^ 

Ni 



K 




Fig. 122. — A central rib of the left side. 
Inferior aspect. 



articulation with the end of the transverse pro- 
cess of the lower of the two vertebrae to w^hich 
the head is connected. The non-articular por- 
tion is a rough elevation, and affords attach- 
ment to the ligament of the tubercle. The 
tubercle is much more prominent in the upper 
than in the lower ribs. 

Body. — The body or shaft is thin and flat, 
with two surfaces, an external and an internal; 
and two borders, a superior and an inferior. 
The external surface is convex, smooth, and 
marked, a little in front of the tubercle, by a 
prominent line, directed downward and lateral- 
ward; this gives attachment to a tendon of 
the lliocostalis, and is called the angle. At 
this point the rib is bent in two directions, 
and at the same time twisted on its long axis. 
If the rib be laid upon its lower border, the 
portion of the body in front of the angle rests 
upon this border, while the portion behind the 
angle is bent medialward and at the same 
time tilted upward; as the result of the twist- 
ing, the external surface, behind the angle, 
looks downward, and in front of the angle, 
slightly upward. The distance between the 
angle and the tubercle is progressively greater 
from the second to the tenth ribs. The por- 
tion between the angle and the tubercle is 
rounded, rough, and irregular, and serves for 
the attachment of the Longissimus dorsi. The 
internal surface is concave, smooth, directed a 
little upward behind the angle, a little down- 
ward in front of it, and is marked by a ridge 
which commences at the lower extremity of 
the head; this ridge is strongly marked as far 
as the angle, and gradually becomes lost at 
the junction of the anterior and middle thirds 
of the bone. Between it and the inferior 
border is a groove, the costal groove, for the 
intercostal vessels and nerve. At the back 
part of the bone, this groove belongs to the 



I 



THE RIBS 



125 



inferior border, but just in front of the angle, where it is deepest and broadest, it is 
on the internal surface. The superior edge of the groove is rounded and serves 
for the attachment of an Intercostalis internus; the inferior edge corresponds to 
the lower margin of the rib, and gi\x>s attachment to an Intercostalis externus. 
Within the groove are seen the orifices of numerous small foramina for nutrient 
vessels which traverse the shaft obliquely from before backward. The superior 
border, thick and rounded, is marked by an external and an internal lip, more 
distinct behind than in front, which serve for the attachment of Intercostales 
externus and internus. The inferior border is thin, and has attached to it an Inter- 
costalis externus. 

Anterior Extremity.— The anterior or sternal extremity is flattened, and presents a 
porous, o\i\\, concave depression, into which the costal cartilage is received. 

Peculiar Ribs.— The first, second, tenth, eleventh, and twelfth ribs present 
certain variations from the common characteristics described above, and require 
special consideration. 

■ Demifacet for vertebra 

Inter articular crest 
Demifacet for vertebra 




Costal groove 



Fig. 123. — A central rib of the left side, viewed from behind. 

First Rib. — The first rib (Fig. 1 24) is the most curved and usually the shortest 
of all the ribs; it is broad and flat, its surfaces looking upward and downward, 
and its borders inward and outward. The head is small, rounded, and possesses 
only a single articular facet, for articulation with the body of the first thoracic 
vertebra. The neck is narrow and rounded. The tubercle, thick and prominent, 
is placed on the outer border. There is no angle, but at the tubercle the rib is 
slightly bent, with the convexity upward, so that the head of the bone is directed 
downward. The upper surface of the body is marked by two shallow grooves, 
separated from each other by a slight ridge prolonged internally into a tubercle, 
the scalene tubercle, for the attachment of the Scalenus anterior; the anterior 
groove transmits the subclavian vein, the posterior the subclavian artery and 
the lowest trunk of the brachial plexus. ^ Behind the posterior groove is a rough 
area for the attachment of the Scalenus medius. The imder surface is smooth, 
and destitute of a costal groove. The outer border is convex, thick, and rounded, 
and at its posterior part gives attachment to the first digitation of the Serratus 
anterior; the inner border is concave, thin, and sharp, and marked about its center 
by the scalene tubercle. The anterior extremity is larger and thicker than that 
of any of the other ribs. 

Second Rib. — The second rib (Fig. 125) is much longer than the first, but has a 
very similar curvature. The non-articular portion of the tubercle is occasionally 



1 Anat. Anzeiger, 1910, Band xxxvi. 



126 



OSTEOLOGY 



only feebly marked. The angle is slight, and situated close to the tubercle. The 
body is not twisted, so that both ends touch any plane surface upon which it may 
be laid; but there is a bend, with its convexity upward, similar to, though smaller 
than that found in the first rib. The body is not flattened horizontally like that 
of the first rib. Its external surface is convex, and looks upward and a little outward ; 
near the middle of it is a rough eminence for the origin of the lower part of the 



Fig. 124 



Angle 




Fig. 126 
Single articular facet — " 

FiQ. 127 
Single articular facet 

Fia. 128 
Single articular facet ■ 




Figs. 124 to 128. — Peculiar ribs. 



first and the whole of the second digitation of the Serratus anterior; behind and 
above this is attached the Scalenus posterior. The internal surface, smooth, and 
concave, is directed downward and a little inward: on its posterior part there is 
a short costal groove. 

Tenth Rib. — The tenth rib (Fig. 126) has only a single articular facet on its head. 

Eleventh and Twelfth Ribs.— The eleventh and twelfth ribs (Figs. 127 and 128) 
have each a single articular facet on the head, which is of rather large size; they 



THE COSTAL CARTILAGES 127 

have 710 necks or tubercles, and are pointed at their anterior ends. The eleventh 
has a slight angle and a shallow costal groove. The twelfth has neither; it is much 
shorter than the eleventh, and its head is inclined slightly downward. Sometimes 
the twelfth rib is even shorter than the first. 

Structure. — The ribs consist of highly vascular cancellous tissue, enclosed in a thin layer of 
compact bone. 

Ossification. — Each rib, with the exception of the last two, is ossified from four centers; a 
primary center for the body, and three epiphysial centers, one for the head and one each for the 
articular and non-articular parts of the tubercle. The eleventh and twelfth ribs have each only 
two centers, those for the tubercles being wanting. Ossification begins near the angle toward the 
end of the second month of fetal life, and is seen first in the sixth and seventh ribs. The epiphyses 
for the head and tubercle make their appearance between the sixteenth and twentieth years, and 
are united to the body about the twenty-fifth year. Fawcett^ states that "in all probability there 
is usually no epiphysis on the non-articular part of the tuberosity below the sixth or seventh rib. 

The Costal Cartilages (Cartilagines Costales). 

The costal cartilages (Fig. 115) are bars of hyaline cartilage which serve to 
prolong the ribs forward and contribute very materially to the elasticity of the 
walls of the thorax. The first seven pairs are connected with the sternum; the 
next three are each articulated with the lower border of the cartilage of the pre- 
ceding rib; the last two have pointed extremities, which end in the wall of the 
abdomen. Like the ribs, the costal cartilages vary in their length, breadth, and 
direction. They increase in length from the first to the seventh, then gradually 
decrease to the twelfth. Their breadth, as well as that of the intervals between 
them, diminishes from the first to the last. They are broad at their attachments 
to the ribs, and taper toward their sternal extremities, excepting the first two, 
which are of the same breadth throughout, and the sixth, seventh, and eighth, 
which are enlarged where their margins are in contact. They also vary in direc- 
tion: the first descends a little, the second is horizontal, the third ascends slightly, 
while the others are angular, following the course of the ribs for a short distance, 
and then ascending to the sternum or preceding cartilage. Each costal cartilage 
presents two surfaces, two borders, and two extremities. 

Surfaces. — The anterior surface is convex, and looks forward and upward: that 
of the first gives attachment to the costoclavicular ligament and the Subclavius 
muscle; those of the first six or seven at their sternal ends, to the Pectoralis major. 
The others are covered by, and give partial attachment to, some of the flat muscles 
of the abdomen. The posterior surface is concave, and directed backward and 
downward; that of the first gives attachment to the Sternothyroideus, those of 
the third to the sixth inclusive to the Trans versus thoracis, and the six or seven 
inferior ones to the Transversus abdominis and the diaphragm. 

Borders. — Of the two borders the superior is concave, the inferior convex; they 
afford attachment to the Intercostales interni : the upper border of the sixth gives 
attachment also to the Pectoralis major. The inferior borders of the sixth, seventh, 
eighth, and ninth cartilages present heel-like projections at the points of greatest 
convexity. These projections carry smooth oblong facets which articulate respec- 
tively with facets on slight projections from the upper borders of the seventh, 
eighth, ninth, and tenth cartilages. 

Extremities. — The lateral end of each cartilage is continuous with the osseous 
tissue of the rib to which it belongs. The medial end of the first is continuous 
with the sternum; the medial ends of the six succeeding ones are rounded and are 
received into shallow concavities on the lateral margins of the sternum. The 
medial ends of the eighth, ninth, and tenth costal cartilages are pointed, and are 
connected each with the cartilage immediately above. Those of the eleventh and 
twelfth are pointed and free. In old age the costal cartilages are prone to undergo 
superficial ossification. 

1 Journal of Anatomy and Physiology, vol. xlv. 



128 



OSTEOLOGY 



Cervical ribs derived from the seventh cervical vertebra (page S3) are of not infrequent occur- 
rence, and are important chnically because they may give rise to obscure nervous or vascular 
symptoms. The cervical rib may be a mere epiphysis articulating only with the transverse process 
of the vertebra, but more commonly it consists of a defined head, neck, and tubercle, with or 
without a body. It extends lateralward, or forward and lateralward, into the postft-ior triangle 
of the neck, where it may terminate in a free end or may join the first thoracic rib, the first costal 
cartilage, or the sternum.^ It varies much in shape, size, direction, and -mobility. If it reach 
far enough forward, part of the brachial plexus and the subclavian artery and vein cross over 
it, and are aj)t to suffer compression in so doing. Pressure on the artery may obstruct the circula- 
tion so much that arterial thrombosis results, causing gangrene of the finger tips. Pressure on 
the nerves is commoner, and affects the eighth cervical and first thoracic nerves, causing paralj'sis 
of the muscles they supply, and neuralgic pains and paresthesia in the area of skin to which they 
are distributed : no oculopupillary changes are to be found. 

The thorax is frequently found to be altered in shape in certain diseases. 

In rickets, the ends of the ribs, where they join the costal cartilages, become enlarged, giving 
rise to the so-caUed "rickety rosary," which in mild cases is only found on the internal surface 
of the thorax. Lateral to these enlargements the softened ribs sink in, so as to i^resent a groove 
passing dowmward and lateralward on either side of the sternum. This bone is forced forward 
by the bending of the ribs, and the antero-posterior diameter of the chest is increased. The ribs 
affected are the second to the eighth, the lower ones being prevented from falling in bj- the pres- 
ence of the liver, stomach, and spleen ; and when the abdomen is distended, as it often is in rickets,, 
the lower ribs may be pushed outward, causing a transverse groove (Harrison's sulcus) just 
above the costal arch. This deformit}'' or forward projection of the sternum, often asymmetrical, 
is known as pigeon breast, and may be taken as evidence of active or old rickets except in cases 
of primary spinal curvatui'e. In many instances it is associated in children with obstruction in 
the upper air passages, due to enlarged tonsils or adenoid growths. In some rickety children or 
adults, and also in others who give no history or further evidence of having had rickets, an opposite 
condition obtains. The lower part of the sternum and often the xiphoid process as well are deeply 
depressed backward, producing an oval hollow in the lower sternal and upper epigastric regions. 
This is known as funnel breast (German, Trichterbrnst); it never appears to produce the least 
disturbance of any of the vital functions. The phthisical chest is often long and narrow, and with 
great obliquity of the ribs and projection of the scapulae. In pulmonary emphysema the chest is 
enlarged in all its diameters, and presents on section an almost circular outline. It has received 
the name of the barrel-shaped chest. In severe cases of lateral curvature of the vertebral column 
the thorax becomes much distorted. In consequence of the rotation of the bodies of the vertebrae 
which takes place in this disease, the ribs opposite the convexity of the dorsal curve become 
extremely convex behind, being thrown out and bulging, and at the same time flattened in front, 
so that the two ends of the same rib are almost parallel. Coincidently with this the ribs on the 
opposite side, on the concavity of the curve, are sunk and depressed behind, and bulging and 
convex in front. 

THE SKULL. 

The skull is supported on the summit of the vertebral column, and is of an 
oval shape, wider behind than in front. It is composed of a series of flattened 
or irregular bones which, with one exception (the mandible), are immovably 
jointed together. It is divisible into two parts: (1) the cranium, which lodges 
and protects the brain, consists of eight bones, and (2) the skeleton of the face, 
of fourteen, as follows: 



Skull, 22 bones 



Cranium, 8 bones 



. Face, 14 bones 



Occipital. 

Two Parietals. 

Frontal. 

Two Temporals. 

Sphenoidal. 

Ethmoidal. 

^ Two Nasals. 

Two :\Iaxillffi. 

Two Lacrimals. 

Two Zygomatics. 

Two Palatines. 

Two Inferior Nasal Conchse. 

Vomer. 
[ ]Mandible. 



> W. Thorburn, The Medical Chronicle, Manchester, 1907, 4th series, xiv, No. 3 



THE OCCIPITAL BONE 



129 



In the Basle nomenclature, certain bones developed in association with the nasal 
capsule, viz., the inferior nasal conchas, the lacrimals, the nasals, and the vomer, 
are grouped as cranial and not as facial bones. 

The hyoid bone, situated at the root of the tongue and attached to the base 
of the skull by ligaments, is described in this section. 



THE CRANIAL BONES (OSSA CRANE). 

The Occipital Bone (Os Occipitale). 

The occipital bone (Figs. 129, 130), situated at the back and lower part of the 
cranium, is trapezoid in shape and curved on itself. It is pierced by a large oval 
aperture, the foramen magnum, through which the cranial cavity communicates 
with the vertebral canal. 



Highest 
mtchal I 




Hypoglossal canal 



Constrictor pharyngis 
superior 



Fig. 129.— Occipital bone. Outer surface. 

The curved, expanded plate behind the foramen magnum is named the squama; 
the thick, somewhat quadrilateral piece in front of the foramen is called the 
basilar part, whilst on either side of the foramen is the lateral portion. 

The Squama {squama occipitalis). — The squama, situated above and behind 
the foramen magnum, is curved from above downward and from side to side. 

Surfaces. — The external surface is convex and presents midway between the 
summit of the bone and the foramen magnum a prominence, the external occipital 
protuberance. Extending lateralward from this on either side are two curved 
lines, one a little above the other. The upper, often faintly marked, is named 
the highest nuchal line, and to it the galea aponeurotica is attached. The lower 
9 



130 



OSTEOLOGY 



is termed the superior nuchal line. That part of the squama which lies above 
the highest nuchal lines is named the planum occipitale, and is covered by the 
Occipitalis muscle; that below, termed the planum nuchale, is rough and irregular 
for the attachment of several muscles. From the external occipital protuberance 
a ridge or crest, the median nuchalline, often faintly marked, descends to the fora- 
men magnum, and affords attachment to the ligamentum nuchae; running from 
the middle of this line across either half of the nuchal plane is the inferior nuchal 
line. Several muscles are attached to the outer surface of the squama, thus: 
the superior nuchal line gives origin to the Occipitalis and Trapezius, and msertion 
to the Sternocleidomastoideus and Splenius capitis: into the surface between 



Su/ien'o . 



S u/i pj. 




Inferior A ngLe 
Fig. 130. — Occipita bone. 

the superior and inferior nuchal lines the Semispinalis capitis and the Obliquus 
capitis superior are inserted, while the inferior nuchal line and the area below 
it receive the insertions of the Recti capitis posteriores major and minor. The 
posterior atlantooccipital membrane is attached around the postero-lateral part 
of the foramen magnum, just outside the margin of the foramen. 

The internal surface is deeply concave and divided into four fossae by a cruciate 
eminence. The upper two fossae are triangular and lodge the occipital lobes of 
the cerebrum; the lower two are quadrilateral and accommodate the hemispheres 
of the cerebellum. At the point of intersection of the four divisions of the cruciate 
eminence is the internal occipital protuberance. From this protuberance the upper 
division of the cruciate eminence runs to the superior angle of the bone, and on 



THE OCCIPITAL BONE 131 

one side of it (generally the right) is a deep groove, the sagittal sulcus, which lodges 
the hinder part of the superior sagittal sinus; to the margins of this sulcus the falx 
cerebri is attached. The lower division of the cruciate eminence is prominent, 
and is named the internal occipital crest; it bifurcates near the foramen magnum 
and gives attachment to the falx cerebelli; in the attached margin of this falx 
is the occipital sinus, which is sometimes duplicated. In the upper part of the 
internal occipital crest, a small depression is sometimes distinguishable; it is 
termed the vermian fossa since it is occupied by part of the vermis of the cerebellum. 
Transverse grooves, one on either side, extend from the internal occipital protuber- 
ance to the lateral angles of the bone; those grooves accommodate the transverse 
sinuses, and their prominent margins give attachment to the tentorium cerebelli. 
The groove on the right side is usually larger than that on the left, and is 
continuous with that for the superior sagittal sinus. Exceptions to this condition 
are, however, not infrequent; the left may be larger than the right or the two 
may be almost equal in size. The angle of union of the superior sagittal and trans- 
verse sinuses is named the confluence of the sinuses {torcular Herophili^), and its 
position is indicated by a depression situated on one or other side of the 
protuberance. 

Lateral Parts {pars lateralis). — The lateral parts are situated at the sides of 
the foramen magnum; on their under surfaces are the condyles for articulation 
with the superior facets of the atlas. The condyles are oval or reniform in shape, 
and their anterior extremities, directed forward and medialward, are closer together 
than their posterior, and encroach on the basilar portion of the bone; the posterior 
extremities extend back to the level of the middle of the foramen magnum. The 
articular surfaces of the condyles are convex from before backward and from 
side to side, and look downward and lateral ward. To their margins are attached 
the capsules of the atlantooccipital articulations, and on the medial side of each 
is a rough impression or tubercle for the alar ligament. At the base of either 
condyle the bone is tunnelled by a short canal, the hypoglossal canal {anterior 
condyloid foramen). This begins on the cranial surface of the bone immediately 
above the foramen magnum, and is directed lateralward and forward above the 
condyle. It may be partially or completely divided into two by a spicule of bone ; 
it gives exit to the hypoglossal or twelfth cerebral nerve, and entrance to a meningeal 
branch of the ascending pharyngeal artery. Behind either condyle is a depression, 
the condyloid fossa, which receives the posterior margin of the superior facet of 
the atlas when the head is bent backward; the floor of this fossa is sometimes 
perforated by the condyloid canal, through which an emissary vein passes from the 
transverse sinus. Extending lateralward from the posterior half of the condyle 
is a quadrilateral plate of bone, the jugular process, excavated in front by the jugular 
notch, which, in the articulated skull, forms the posterior part of the jugular fora- 
men. The jugular notch may be divided into two by a bony spicule, the intra- 
jugular process, which projects lateralward above the hypoglossal canal. The 
under surface of the jugular process is rough, and gives attachment to the Rectus 
capitis lateralis muscle and the lateral atlantooccipital ligament; from this 
surface an eminence, the paramastoid process, sometimes projects downward, and 
may be of sufficient length to reach, and articulate with, the transverse process 
of the atlas. Laterally the jugular process presents a rough quadrilateral or tri- 
angular area which is joined to the jugular surface of the temporal bone by a plate 
of cartilage; after the age of twenty-five this plate tends to ossify. 

The upper surface of the lateral part presents an oval eminence, the jugular 
tubercle, which overlies the hypoglossal canal and is sometimes crossed by an 
oblique groove for the glossopharyngeal, vagus, and accessory nerves. On the 

' The columns of blood coming in different directions were supposed to be pressed together at this point {iorcular. 
a wine press). 



132 



OSTEOLOGY 



upper surface of the jugular process is a deep groove which curves medialward 
and forward and is continuous with the jugular notch. This groove lodges the 
terminal part of the transverse sinus, and opening into it, close to its medial 
margin, is the orifice of the condyloid canal. 

Basilar Part (pars basilaris). — The basilar part extends forward and upward 
from the foramen magnum, and presents in front an area more or less quadrilateral 
in outline. In the young skull this area is rough and uneven, and is joined to the 
body of the sphenoid by a plate of cartilage. By the twenty-fifth year this cartil- 
aginous plate is ossified, and the occipital and sphenoid form a continuous bone. 
Surfaces. — On its lower surface, about 1 cm. in front of the foramen magnum, 
is the pharyngeal tubercle which gives attachment to the fibrous raphe of the pharynx. 
On either side of the middle line the Longus capitis and Rectus capitis anterior 
are inserted, and immediately in front of the foramen magnum the anterior 
atlantooccipital membrane is attached. 

The upper surface presents a broad, shallow groove Avhich inclines upward 
and forward from the foramen magnum; it supports the medulla oblongata, and 
near the margin of the foramen magnum gives attachment to the membrana 
tectoria. On the lateral margins of this surface are faint grooves for the inferior 
petrosal sinuses. 

Foramen Magnum. — The foramen magnum is a large oval aperture with its long 
diameter antero-posterior ; it is wider behind than in front where it is encroached 
upon by the condyles. It transmits the medulla oblongata and its membranes, 
the accessory nerves, the vertebral arteries, the anterior and posterior spinal 
arteries, and the membrana tectoria and alar ligaments. 

Angles. — The superior angle of the occipital bone articulates with the occipital 
angles of the parietal bones and, in the fetal skull, corresponds in position with the 
posterior fontanelle. The inferior angle is fused with the body of the sphenoid. 
The lateral angles are situated at the extremities of the grooves for the transverse 

sinuses: each is received into the interval 
between the mastoid angle of the parietal 
and the mastoid part of the temporal. 

Borders. — The superior borders extend 
from the superior to the lateral angles: 
thej" are deeply serrated for articulation 
with the occipital borders of the parietals, 
and form by this union the lambdoidal 
suture. The inferior borders extend from 
the lateral angles to the inferior angle; 
the upper half of each articulates with 
the mastoid portion of the corresponding 
temporal, the lower half with the petrous 
part of the same bone. These two por- 
tions of the inferior border are separated 
from one another by the jugular process, 
the notch on the anterior surface of which 
forms the posterior part of the jugular 
foramen. 

Fig. 131. — Occipital bone at birth. 

Structure. — The occipital, like the other cranial 

bones, consists of two compact lamellae, called 

the outer and inner tables, between which is the cancellous tissue or diploe; the bone is especially 

thick at the ridges, protuberances, condyles, and anterior part of the basilar part; in the inferior 

fossge it is thin, semitransparent, and destitute of diploe. 

Ossification (Fig. 131). — The planum occipitale of the squama is developed in membrane, 
and may remain separate throughout life when it constitutes the interparietal bone; the rest of 




Planum 
< ccipitale 



Planum 
imcfiale 

Kerckring's 
center 

Lateral 
part 



Basilar part 



1 



THE PARIETAL BONE 



133 



the bone is developed in cartilage. The number of nuclei for the planum occipitale is usually 
given as four, two appearing near the middle line about the second month, and two some little 
distance from the middle line about the third month of fetal life. The planum nuchalc of the 
squama is ossified from two centers, which appear about the seventh week of fetal life and soon 
unite to form a single piece. Union of the upper and lower portions of the squama takes place 
in the third month of fetal life. An occasional center (Kerckring) appears in the posterior margin 
of the foramen magnum dm'ing the fifth month; this forms a separate ossicle (sometimes double) 
which unites with the rest of the squama before birth. Each of the lateral parts begins to 
ossify from a single center during the eighth week of fetal hfe. The basilar portion is ossified 
from two centers, one in front of the other; these appear about the sixth week of fetal life and 
rapidly coalesce. Mall' states that the planum occipitale is ossified from two centers and the 
basilar portion from one. About the fourth year the squama and the two lateral portions unite, 
and about the sixth year the bone consists of a single piece. Between the eighteenth and twenty- 
fifth years the occipital and sphenoid become united, forming a single bone. 

Articulations.^The occipital articulates with six bones: the two parietals, the two temporals, 
the sphenoid, and the atlas. 



The Parietal Bone (Os Parietale). 

The parietal bones form, by their union, the sides and roof of the cranium. Each 
bone is irregularly quadrilateral in form, and has two surfaces, four borders, 
and four angles. 

Articulates with opposite parietal bone 




With sphenoid 



With mastoid portion of 
temvoral bone 



Fig. 132. — -Left parietal bone. Outer surface. 



Surfaces.— The external surface (Fig. 132) is convex, smooth, and marked near 
the center by an eminence, the parietal eminence {tuber paridale), which indicates 
the point where ossification commenced. Crossing the middle of the bone in an 

• American Journal of Anatomy, 1906, vol. v. 



134 



OSTEOLOGY 



arched direction are two curved lines, the superior and inferior temporal lines; the 
former gives attachment to the temporal fascia, and the latter indicates the upper 
limit of the muscular origin of the Temporalis. Above these lines the bone is 
covered by the galea aponeurotica ; below them it forms part of the temporal 
fossa, and affords attachment to the Temporalis muscle. At the back part and 
close to the upper or sagittal border is the parietal foramen, which transmits a 
vein to the superior sagittal sinus, and sometimes a small brancli of the occipital 
artery; it is not constantly present, and its size varies considerably. 

The internal surface (Fig. 133) is concave; it presents depressions corresponding 
to the cerebral convolutions, and numerous furrows for the ramifications of the 
middle meningeal vessel;^ the latter run upward and backward from the sphenoidal 
angle, and from the central and posterior part of the squamous border. Along 
the upper margin is a shallow groove, which, together with that on the opposite 



!^^m^f^bA',. 



Occipital , r'~-\^Jf 

angle [ '■/\^ 



;'"'-... I. J'^'onial 
angle 



Mastoid 
angle 




Sphenoidal angle 



Fig. 133. — Left parietal bone. Inner surface. 



parietal, forms a channel, the sagittal sulcus, for the superior sagittal sinus; the 
edges of the sulcus afford attachment to the falx cerebri. Near the groove are 
several depressions, best marked in the skulls of old persons, for the arachnoid 
granulations {Pacchionian bodies). In the groove is the internal opening of the 
parietal foramen when that aperture exists. 

Borders. — The sagittal border, the longest and thickest, is dentated and articu- 
lates with its fellow of the opposite side, forming the sagittal suture. The squamous 
border is divided into three parts: of these, the anterior is thin and pointed, bevelled 
at the expense of the outer surface, and overlapped by the tip of the great wing 
of the sphenoid; the middle portion is arched, bevelled at the expense of the outer 
surface, and overlapped by the squama of the temporal; the posterior part is thick 
and serrated for articulation with the mastoid portion of the temporal. The 

» Journal of Anatomy and Physiology, 1912, vol. xlvi. 



THE FRONTAL BONE 135 

frontal border is deeply serrated, and bevelled at the expense of the outer surface 
above and of the inner below; it articulates with the frontal bone, forming one- 
half of the coronal suture. The occipital border, deeply denticulated, articulates 
with the occipital, forming one-half of the lambdoidal suture. 

Angles.— The frontal angle is practically a right angle, and corresponds with 
the point of meeting of the sagittal and coronal sutures; this point is named the 
bregma; in the fetal skull and for about a year and a half after birth this region is 
membranous, and is called the anterior fontanelle. The sphenoidal angle, thin 
and acute, is received into the interval between the frontal bone and the great 
wing of the sphenoid. Its inner surface is marked by a deep groove, sometimes 
a canal, for the anterior divisions of the middle meningeal artery. The occipital 
angle is rounded and corresponds with the point of meeting of the sagittal and 
lambdoidal sutures— a point which is termed the lambda; in the fetus this part 
of the skull is membranous, and is called the posterior fontanelle. The mastoid 
angle is truncated; it articulates with the occipital bone and with the mastoid 
portion of the temporal, and presents on its inner surface a broad, shallow groove 
which lodges part of the transverse sinus. The point of meeting of this angle 
with the occipital and the mastoid part of the temporal is named the asterion. 

Ossification. — The parietal bone is ossified in membrane from a single center, which appears 
at the parietal eminence about the eighth week of fetal life. Ossification gradually extends in 
a radial manner from the center toward the margins of the bone; the angles are consequently 
the parts last formed, and it is here that the fontanelles exist. Occasionally the parietal bone 
is divided into two parts, upper and lower, by an antero-posterior suture. 

Articulations. — The parietal articulates with five bones: the opposite parietal, the occipital, 
frontal, temporal, and sphenoid. 

The Frontal Bone (Os Frontale). 

The frontal bone resembles a cockle-shell in form, and consists of two portions 
— a vertical portion, the squama, corresponding with the region of the forehead; 
and an orbital or horizontal portion, which enters into the formation of the roofs 
of the orbital and nasal cavities. 

Squama {squama frontalis). — Surfaces. — The external surface (Fig. 134) of this 
portion is convex and usually exliibits, in the lower part of the middle line, the 
remains of the frontal or metopic suture; in infancy this suture divides the bone into 
two, a condition which may persist throughout life. On either side of this suture, 
about 3 cm. above the supraorbital margin, is a rounded elevation, the frontal emi- 
nence (tuber frontale). These eminences vary in size in different individuals, are 
occasionally unsymmetrical, and are especially prominent in young skulls; the sur- 
face of the bone above them is smooth, and covered by the galea aponeurotica. 
Below the frontal eminences, and separated from them by a shallow groove, are 
two arched elevations, the superciliary arches; these are prominent medially, and 
are joined to one another by a smooth elevation named the glabella. They are 
larger in the male than in the female, and their degree of prominence depends 
to some extent on the size of the frontal air sinuses;^ prominent ridges are, how- 
ever, occasionally associated with small air sinuses. Beneath each superciliary 
arch is a curved and prominent margin, the supraorbital margin, Avliich forms the 
upper boundary of the base of the orbit, and separates the squama from the orbital 
portion of the bone. The lateral part of this margin is sharp and prominent, 
affording to the eye, in that situation, considerable protection from injury; the 
medial part is rounded. At the junction of its medial and intermediate thirds is 

1 Some confusion is occasioned to students commencing the study of anatomy by the name "sinus" having been 
given to two different kinds of space connected with the skull. It may be as well, therefore, to state here that the 
"sinuses" in the interior of the cranium which produce the grooves on the inner surfaces of the bones are venous 
channels which convey the Ijlood from the brain, while the "sinuses" external to the cranial cavity (the frontal, 
sphenoidal, ethmoidal, and maxillary) are hollow spaces in the bones themselves; they communicate with the nasal 
javities and contain air. 



136 



OSTEOLOGY 



a notch, sometimes converted into a foramen, the supraorbital notch or foramen, 
which transmits the supraorbital vessels and nerve. A small aperture in the upper 
part of the notch transmits a vein from the diploe to join the supraorbital vein. 
The supraorbital margin ends laterally in the zygomatic process, which is strong 
and prominent, and articulates with the zygomatic bone. Running upward and 
backward from this process is a well-marked line, the temporal line, which divides 
into the upper and lower temporal lines, continuous, in the articulated skull, with 
the corresponding lines on the parietal bone. The area below and behind the tem- 
poral line forms the anterior part of the temporal fossa, and gives origin to the 
Temporalis muscle. Between the supraorbital margins the squama projects down- 
ward to a level below that of the zygomatic processes; this portion is known as the 
nasal part and presents a rough, uneven interval, the nasal notch, which articulates 




Zygomatic 
process 



Frontal I spine 
Fig. 134. — Frontal bone. Outer surface. 



on either side of the middle line with the nasal bone, and laterally with the frontal 
process of the maxilla and with the lacrimal. The term nasion is applied to the 
middle of the frontonasal suture. From the center of the notch the nasal process 
projects downward and forwon] beneath the nasal bones and frontal processes of 
the maxillae, and supports the bridge of the nose. The nasal process ends below 
in a sharp spine, and on either side of this is a small grooved surface which enters 
into the formation of the roof of the corresponding nasal cavity. The spine forms 
part of the septum of the nose, articulating in front with the crest of the nasal 
bones and behind with the perpendicular plate of the ethmoid. 

The internal siirface (Fig. 1.35) of the squama is concave and presents in the 
upper part of the middle line a vertical groove, the sagittal sulcus, the edges of 
which unite below to form a ridge, the frontal crest; the sulcus lodges the superior 
sagittal sinus, while its margins and the crest afford attachment to the falx cerebri. 



THE FRONTAL BONE 



137 



The crest ends below in a small notch which is converted into a foramen, the fora- 
men cecum, by articulation with the ethmoid. This foramen varies in size in 
different subjects, and is frequently impervious; when open, it transmits a vein 
from the nose to the superior sagittal sinus. On either side of the middle line the 
bone presents depressions for the convolutions of the brain, and numerous small 
furrows for the anterior branches of the middle meningeal vessels. Se\eral small, 
irregular fossae may also be seen on either side of the sagittal sulcus, for the 
reception of the arachnoid granulations. 

Orbital or Horizontal Part {pars orbitalis) .—This portion consists of two thin 
triangular plates, the orbital plates, which form the vaults of the orbits, and are 
separated from one another by a median gap, the ethmoidal notch. 







Supraorbital 
foramen 



With maxilla 

With nasal ^ I 
With 'perpendicular plate of ethmoid 



Frontal sinus 



Under surface of nasal process 
forming part of roof of nose 



Fig. 135. — Frontal bone. Inner surface. 



Surfaces. — The inferior surface (Fig. 135) of each orbital plate is smooth and 
concave, and presents, laterally, under cover of the zygomatic process, a shallow 
depression, the lacrimal fossa, for the lacrimal gland; near the nasal part is a depres- 
sion, the fovea trochlearis, or occasionally a small trochlear spine, for the attach- 
ment of the cartilaginous pulley of the Obliquus oculi superior. The superior 
surface is convex, and marked by depressions for the convolutions of the frontal 
lobes of the brain, and faint grooves for the meningeal branches of the ethmoidal 
vessels. 

The ethmoidal notch separates the two orbital plates; it is quadrilateral, and 
filled, in the articulated skull, by the cribriform plate of the ethmoid. The margins 
of the notch present several half-cells which, when united with corresponding 
half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells. 
Two grooves cross these edges transversely; they are converted into the anterior 



138 



OSTEOLOGY 



and posterior ethmoidal canals by the ethmoid, and open on the medial wall of the 
orbit. The anterior canal transmits the nasociliary nerve and anterior ethmoidal 
vessels, the posterior, the posterior ethmoidal nerve and vessels. In front of the 
ethmoidal notch, on either side of the frontal spine, are the openings of the frontal . 
air sinuses. These are two irregular cavities, which extend backward, upward, 
and lateralward for a variable distance between the two tables of the skull; they 
are separated from one another by a thin bony septum, which often deviates to 
one or other side, Avith the result that the sinuses are rarelv svmmetrical. Absent 
at birth, they are usually fairly well-developed between the seventh and eighth 
years, but only reach their full size after puberty. They vary in size in different 
persons, and are larger in men than in women. ^ They are lined by mucous mem- 
brane, and each communicates with the corresponding nasal cavity by means of a 
passage called the frontonasal duct. 

Borders. — The border of the squama is thick, strongly serrated, bevelled at the 
expense of the inner table above, where it rests upon the parietal bones, and at 
the expense of the outer table on either side, where it receives the lateral pressure 
of those bones; this border is continued below into a triangular, rough surface, 
which articulates with the great wing of the sphenoid. The posterior borders of 
the orbital plates are thin and serrated, and articulate with the small wings of the 
sphenoid. 

Structure. — ^The squama and the zj^gomatic processes are very thick, consisting of diploic 
tissue contained between two compact lamina?; the diploic tissue is absent in the regions occupied 
by the frontal air sinuses. The orbital portion is thin, translucent, and (Composed entirely of 
compact bone; hence the faciUty with which instruments can penetrate the cranium through 
this part of the orbit; when the frontal sinuses are exceptionally large they may extend backward 
for a considerable distance into the orbital portion, which in such cases also consists of only two 
tables. 

Ossification (Fig. 136). — The frontal bone is ossified in membrane from tivo primary 
centers, one for each half, which appear toward the end of the second month of fetal life, one 
above each supraorbital margin. From each of these centers ossification extends upward to form 
the corresponding half of the squama, and backward to form the orbital plate. The spine is 

ossified from a pair of secondary centers, 
on either side of the middle line; similar 
centers appear in the nasal part and zygo- 
matic processes. At birth the bone consists 
of two pieces, separated by the frontal 
suture, which is usually obUterated, except 
at its lower part, by the eighth year, but 
occasionally persists throughout Ufe. It is 
generally maintained that the development 
of the frontal sinuses begins at the end of 
the first or beginning of the second year, 
but Onodi's researches indicate that de- 
velopment begins at birth. The sinuses 
are of considerable size by the seventh or 
eighth year, but do not attain their full 
proportions until after puberty. 

Articulations. — The frontal articulates 
with twelve bones: the sphenoid, the eth- 
moid, the two parietals, the two nasals, the 
two maxillse, the two lacrimals, and the 
two zygomatics. 



.9, 



quama 




Nasal part 



Zygomatic process 



Spine 
Fig. 136. — Frontal bone at birth. 



The Temporal Bone (Os Temporale). 

The temporal bones are situated at the sides and base of the skull. Each consists 
of live parts, viz., the squama, the petrous, mastoid, and tympanic parts, and the 
styloid process. 

1 Aldren Turner (The Accessory Sinuses of the Nose, 1901) gives the following measurements for a sinus of average 
size: height, 13€ inches; breadth, 1 inch; depth from before backward, 1 inch. 



THE TEMPORAL BONE 



139 



The Squama {squama temporalis) .—The squama forms the anterior and upper 
part of the bone, and is scale-hke, thin, and translucent. 

Surfaces.— Its outer surface (Fig. 137) is smooth and convex; it affords attach- 
ment to the TemporaHs muscle, and forms part of the temporal fossa; on its hinder 
part is a vertical groove for the middle temporal artery. A curved line, the tem- 
poral line, or supramastoid crest, runs backward and upward across its posterior 
part; it serves for the attachment of the temporal fascia, and limits the origin 
of the Temporalis muscle. The boundary between the squama and the mastoid 
portion of the bone, as indicated by traces of the original suture, lies about 1 cm. 
below this line. Projecting from the lower part of the squama is a long, arched 
process, the zygomatic process. This process is at first directed lateralward, its 
two surfaces looking upward and downward; it then appears as if twisted inward 



Croove for middle 
temporal artery 



Parietal notch 

Suprameatal 
triangle 

Occipitalis 




Articular tubercle 
Post-glenoid process 

31andih ula r fossa 



Petrotympanic fissure 
Vaginal process 

Styloglossus 



Tympanic part 
Stylohyoideus 

Styloid process 
Fia. 137. — Left temporal bone. Outer surface. 



Occipital groove 



upon itself, and runs forward, its surfaces now looking medial ward and lateralward. 
The superior border is long, thin, and sharp, and serves for the attachment of the 
temporal fascia; the inferior, short, thick, and arched, has attached to it some 
fibers of the Masseter. The lateral surface is convex and subcutaneous ; the medial 
is concave, and affords attachment to the Masseter. The anterior end is deeply 
serrated and articulates with the zygomatic bone. The posterior end is connected 
to the squama by two roots, the anterior and posterior roots. The posterior root, a 
prolongation of the upper border, is strongly marked ; it runs backward above the 
external acoustic meatus, and is continuous with the temporal line. The anterior 
root, continuous with the lower border, is short but broad and strong; it is directed 
medialward and ends in a rounded eminence, the articular tubercle (eminentia 
articularis) . This tubercle forms the front boundary of the mandibular fossa, 



140 



OSTEOLOGY 



and in the fresh state is covered with cartilage. In front of the articular tubercle 
is a small triangular area which assists in forming the infratemporal fossa; this 
area is separated from the outer surface of the squama by a ridge which is continu- 
ous behind with the anterior root of the zygomatic process, and in front, in the 
articulated skull, with the infratemporal crest on the great wing of the sphenoid. 
Between the posterior wall of the external acoustic meatus and the posterior root 
of the zygomatic process is the area called the suprameatal triangle (Macewen), 
or mastoid fossa, through which an instrument may be pushed into the tympanic 
antrum. At the junction of the anterior root with the zygomatic process is a pro- 
jection for the attachment of the temporomandibular ligament; and behind the 
anterior root is an oval depression, forming part of the mandibular fossa, for the 
reception of the condyle of the mandible. The mandibular fossa {glenoid fossa) 



ctal iofii 



Parietal 
nolch 




Eminentia 
nrcuata 



I 

Mastoid foramen 

Aquoeductus vcstihuli 

Aquoediictus cochlcce 

Internal acoustic meatus 
Fig. 138. — Left temporal bone. Inner surface. 

is bounded, in front, by the articular tubercle; behind, by the tympanic part of 
the bone, which separates it from the external acoustic meatus; it is divided into 
two parts by a narrow slit, the petrotympanic fissure {Glaserian fissure). The 
anterior part, formed by the squama, is smooth, covered in the fresh state with 
cartilage, and articulates with the condyle of the mandible. Behind this part 
of the fossa is a small conical eminence; this is the representative of a prominent 
tubercle which, in some mammals, descends behind the condyle of the mandible, 
and prevents its backward displacement. The posterior part of the mandibular 
fossa, formed by the tympanic part of the bone, is non-articular, and sometimes 
lodges a portion of the parotid gland. The petrotympanic fissure leads into the 
middle ear or tympanic cavity; it lodges the anterior process of the malleus, and 
transmits the tympanic branch of the internal maxillary artery. The chorda 



1 



THE TEMPORAL BONE 



141 



tympani nerve passes through a canal {canal of Huguier), separated from the an- 
terior edge of the petrotympanic fissure by a thin scale of bone and situated on 
the lateral side of the auditory tube, in the retiring angle between the squama 
and the petrous portion of the temporal. 

The internal surface of the squama (Fig. 138) is concave; it presents depressions 
corresponding to the convolutions of the temporal lobe of the brain, and grooves 
for the branches of the middle meningeal vessels. 

Borders.— The superior border is thin, and bevelled at the expense of the internal 
table, so as to overlap the squamous border of the parietal bone, forming with 
it the squamosal suture. Posteriorly, the superior border forms an angle, the 
parietal notch, with the mastoid portion of the bone. The antero-inferior border 
is thick, serrated, and bevelled at the expense of the inner table above and of 
the outer below, for articulation with the great wing of the sphenoid. 

Mastoid Portion {pars mastoidea) .—The mastoid portion forms the posterior 
part of the bone. 



Tympanic antrum 



Tegmen tympani 

Prominence of lateral semicircular canal 
Prominence of facial canal 
Fenestra vestihuli 
Bristle in semicanal for Terisor tympani 
Septum canal is muscvlotubarii 
Bristle in hiatus of facial canal 




Carotid canal 

Bony part of auditory tube 
Promontory 
Bristle in pyramid 
Fenestra cochleoe 



Sulctis tympanicus 
Mastoid cells ^^^^^^^ *** stylomastoid foramen 
Fig. 139. — Coronal section of right temporal bone. 



Surfaces. — Its outer surface (Fig. 137) is rough, and gives attachment to the 
Occipitalis and Auricularis posterior. It is perforated by numerous foramina; one 
of these, of large size, situated near the posterior border, is termed the mastoid 
foramen; it transmits a vein to the transverse sinus and a small branch of the occipi- 
tal artery to the dura mater. The position and size of this foramen are very 
variable; it is not always present; sometimes it is situated in the occipital bone, 
or in the suture between the temporal and the occipital. The mastoid portion is 
continued below into a conical projection, the mastoid process, the size and form 
of which vary somewhat; it is larger in the male than in the female. This process 
serves for the attachment of the Sternocleidomastoideus, Splenius capitis, and 
Longissimus capitis. On the medial side of the process is a deep groove, the 
mastoid notch {digastric fossa), for the attachment of the Digastricus; medial to 
this is a shallow furrow, the occipital groove, which lodges the occipital artery. 



142 OSTEOLOGY 

The inner surface of the mastoid portion presents a deep, curved groove, the 
sigmoid sulcus, which lodges part of the transverse sinus; in it may be seen the 
opening of the mastoid foramen. The groove for the transverse sinus is separated 
from the innermost of the mastoid air cells by a very thin lamina of bone, and even 
this may be partly deficient. . 

Borders. — The superior border of the mastoid portion is broad and serrated, for 
articulation with the mastoid angle of the parietal. The posterior border, also 
serrated, articulates with the inferior border of the occipital between the lateral 
angle and jugular process. Anteriorly the mastoid portion is fused with the 
descending process of the squama above; below it enters into the formation of 
the external acoustic meatus and the tympanic cavity. 

A section of the mastoid process (Fig. 139) shows it to be hollowed out into a 
number of spaces, the mastoid cells, which exliibit the greatest possible variety 
as to their size and number. At the upper and front part of the process they are 
large and irregular and contain air, but toward the lower part they diminish in 
size, while those at the apex of the process are frequently quite small and contain 
marrow; occasionally they are entirely absent, and the mastoid is then solid 
throughout. In addition to these a large irregular cavity is situated at the upper 
and front part of the bone. It is called the tympanic antrum, and must be distin- 
guished from the mastoid cells, though it communicates with them. Like the mas- 
toid cells it is filled with air and lined by a prolongation of the mucous membrane 
of the tympanic cavity, with which it communicates. The tympanic antrum is 
bounded above by a thin plate of bone, the tegmen tympani, which separates it 
from the middle fossa of the base of the skull; below by the mastoid process; later- 
ally by the squama just below the temporal line, and medially by the lateral semi- 
circular canal of the internal ear which projects into its cavity. It opens in front 
into that portion of the tympanic cavity which is known as the attic or epitympanic 
recess. The tympanic antrum is a cavity of some considerable size at the time of 
birth; the mastoid air cells may be regarded as diverticula from the antrum, 
and begin to appear at or before birth; by the fifth year they are well-marked, 
but their development is not completed until toward puberty. 

Petrous Portion {pars pefrosa [pyramis]). — The petrous portion or pyramid is 
pyramidal and is wedged in at the base of the skull between the sphenoid and 
occipital. Directed medialward, forward, and a little upward, it presents for 
examination a base, an apex, three surfaces, and three angles, and contains, in 
its interior, the essential parts of the organ of hearing. 

Base. — The base is fused with the internal surfaces of the squama and mastoid 
portion. 

Apex. — The apex, rough and uneven, is received into the angular interval between 
the posterior border of the great wing of the sphenoid and the basilar part of the 
occipital; it presents the anterior or internal orifice of the carotid canal, and 
forms the postero-lateral boundary of the foramen lacerum. 

.Siu-faces. — The anterior surface forms the posterior part of the middle fossa of 
the base of the skull, and is continuous with the imier surface of the squamous 
portion, to which it is united by the petrosquamous suture, remains of which are 
distinct even at a late period of life. It is marked by depressions for the convolu- 
tions of the brain, and presents six points for examination: (1) near the center, 
an eminence {eminentia arcuata) which indicates the situation of the superior semi- 
circular canal; (2) in front of and a little lateral to this eminence, a depression indi- 
cating the position of the tympanic cavity : here the layer of bone which separates 
the tympanic from the cranial cavity is extremely thin, and is known as the 
tegmen tympani; (3) a shallow groove, sometimes double, leading lateralward and 
backward to an oblique opening, the hiatus of the facial canal, for the passage of 
the greater superficial petrosal nerve and the petrosal branch of the middle men- 



THE TEMPORAL BONE 



143 



ingeal artery; (4) lateral to the hiatus, a smaller opening, occasionally seen, for 
the passage of the lesser superficial petrosal nerve; (5) near the apex of the bone, 
the termination of the carotid canal, the wall of which in this situation is deficient 
in front; (6) above this canal the shallow trigeminal impression for the reception 
of the semilunar ganglion. 

The posterior surface (Fig. 1.38) forms the front part of the posterior fossa of 
the base of the skull, and is continuous with the inner surface of the mastoid 
portion. Near the center is a large orifice, the internal acoustic meatus, the size of 
which varies considerably; its margins are smooth and rounded, and it leads into 
a short canal, about 1 cm. in length, which runs lateralward. It transmits the 
facial and acoustic nerves and the internal auditory branch of the basilar artery. 
The lateral end of the canal is closed by a vertical plate, which is divided by a 
horizontal crest, the crista falciformis, into two unequal portions (Fig. 140). Each 
portion is further subdivided by a vertical ridge into an anterior and a posterior 
part. In the portion beneath the crista falciformis are three sets of foramina; 
one group, just below the posterior part of 

the crest, situated in the area cribrosa media, ■> ' 

consists of several small openings for the 
nerves to the saccule; below and behind this 
area is the foramen singulare, or opening for 
the nerve to the posterior semicircular duct; 
in front of and below the first is the tractus 
spiralis foraminosus, consisting of a number of 
small spirally arranged openings, which encircle 
the canalis centralis cochleae; these openings 
together with this central canal transmit the 
nerves to the cochlea. The portion above 
the crista falciformis presents behind, the 
area •cribrosa superior, pierced by a series of 
small openings, for the passage of the nerves 
to the utricle and the superior and lateral 
semicircular ducts, and, in front, the area 
faciaiis, with one large opening, the com- 
mencement of the canal for the facial nerve 
(aquseductus FaUopii). Behind the internal 
acoustic meatus is a small slit almost hidden 
by a thin plate of bone, leading to a canal, 
the aquaeductus vestibuli, which transmits the 
ductus endolymphaticus together with a small artery and vein. Above and 
between these two openings is an irregular depression which lodges a process of 
the dura mater and transmits a small vein; in the infant this depression is repre- 
sented by a large fossa, the subarcuate fossa, which extends backward as a blind 
tunnel under the superior semicircular canal. 

The inferior surface (Fig. 141) is rough and irregular, and forms part of the 
exterior of the base of the skull. It presents eleven points for examination: (1) 
near the apex is a rough surface, quadrilateral in form, which serves partly for the 
attachment of the Levator veli palatini and the cartilaginous portion of the audi- 
tory tube, and partly for connection with the basilar part of the occipital bone 
through the intervention of some dense fibrous tissue; (2) behind this is the large 
circular aperture of the carotid canal, which ascends at first vertically, and then, 
making a bend, runs horizontally forward and medialward; it transmits into the 
cranium the internal carotid artery, and the carotid plexus of nerves; (3) medial 
to the opening for the carotid canal and close to its posterior border, in front of the 
jugular fossa, is a triangular depression; at the apex of this is a small opening, the 




Fig. 140. — Diagrammatic view of the fundus 
of the right internal acoustic meatus. (Testut.) 
1. Crista falciformis. 2. Area facialis, with (2') 
internal opening of the facial canal. 3. Ridge 
separating the area facialis from the area crib- 
rosa superior. 4. Area cribrosa superior, with 
(4') openings for nerve filaments. 5. Anterior 
inferior cribriform area, with (o') the tractus 
spiralis foraminosus, and (5") the canalis cen- 
tralis of the cochlea. 6. Ridge separating the 
tractus spiralis foraminosus from the area crib- 
rosa media. 7. Area cribrosa media, with (7') 
orifices for nerves to saccule. 8. Foramen 
singulare. 



144 



OSTEOLOGY 



aquaeductus cochleae, which lodges a tubular prolongation of the dura mater establish- 
ing a communication between the peril ^inphatic space and the subarachnoid space, 
and transmits a vein from the cochlea to join the internal jugular; (4) behind these 
openings is a deep depression, the jugular fossa, of variable depth and size in different 
skulls; it lodges the bulb of the internal jugular vein; (5) in the bony ridge dividing 
the carotid canal from the jugular fossa is the small inferior tympanic canaliculus 
for the passage of the tympanic branch of the glossopharyngeal nerve; (6) in the 
lateral part of the jugular fossa is the mastoid canaliculus for the entrance of the 
auricular branch of the vagus nerve; (7) behind the jugular fossa is a quadrilateral 
area, the jugular surface, covered with cartilage in the fresh state, and articulating 
wuth the jugular process of the occipital bone; (8) extending backward from the 
carotid canal is the vaginal process, a sheath-like plate of bone, which divides 

Semicanals for 

auditory 

tube and 

Tensor 

tympani 



Lev. veli palatini 

Rough quadrilateral surface 

Opening of carotid canal 

Inferior tympanic canaliculus — 

Aqvcpduchis cochlece 

3Iastoid canaliculus 

Jugular fossa 

Vaginal process 

Styloid process 

Stylomastoid foramen 

Jugidar surface 

Tympanomastoid fissure 




Slylopharyngeus 



Fig. 141. — Left temporal bone. Inferior surface. 

behind into two laminae; the lateral lamina is continuous with the tympanic part 
of the bone, the medial with the lateral margin of the jugular surface; (9) between 
.these laminae is the styloid process, a sharp spine, about 2.5 cm. in length; (10) 
between the styloid and mastoid processes is the stylomastoid foramen; it is the 
termination of the facial canal, and transmits the facial nerve and stylomastoid 
artery; (11) situated between the tympanic portion and the mastoid process is the 
tympanomastoid fissure, for the exit of the auricular branch of the vagus nerve. 
Angles. — The superior angle, the longest, is grooved for the superior petrosal 
sinus, and gives attachment to the tentorium cerebelli; at its medial extremity 
is a notch, in which the trigeminal nerve lies. The posterior angle is intermediate 
in length between the superior and the anterior. Its medial half is marked by 
a sulcus, which forms, with a corresponding sulcus on the occipital bone, the 
channel for the inferior petrosal sinus. Its lateral half presents an excavation 
— the jugular fossa — which, with the jugular notch on the occipital, forms the 



THE TEMPORAL BONE 145 

jugular foramen ; an eminence occasionally projects from the center of the fossa, 
and divides the foramen into two. The anterior angle is divided into two parts 
—a lateral joined to the squama by a suture (petnmiimmotts), the remains of which 
are more or less distinct; a medial, free, which articulates with the spinous process 
of the sphenoid. 

At the angle of junction of the petrous part and the squama are two canals, 
one above the other, and separated by a thin plate of bone, the septum canalis 
musculotubarii (processus cochleariformis); both canals lead into the tympanic 
cavity. The upper one (semicanalis m. tensoris tympani) transmits the Tensor 
tympani, the lower one {semicanalis tuhco anditivw) forms the bony part of the 
auditory tube. 

The tympanic cavity, auditory ossicles, and internal ear, are described with 
the organ of hearing. 

Tympanic Part (pars tympanica). — The tympanic part is a curved plate of bone 
lying below the squama and in front of the mastoid process. 

Surfaces. — Its postero-superior surface is concave, and forms the anterior wall, 
the floor, and part of the posterior wall of the bony external acoustic meatus. 
Medially, it presents a narrow furrow, the tympanic sulcus, for the attachment 
of the tympanic membrane. Its antero-inferior surface is quadrilateral and slightly 
concave; it constitutes the posterior boundary of the mandibular fossa, and is 
in contact with the retromandibular part of the parotid gland. 

Borders. — Its lateral border is free and rough, and gives attachment to the car- 
tilaginous part of the external acoustic meatus. Internally, the tympanic part 
is fused with the petrous portion, and appears in the retreating angle between 
it and the squama, where it lies below and lateral to the orifice of the auditory 
tube. Posteriorly, it blends with the squama and mastoid part, and forms the 
anterior boundary of the tympanomastoid fissure. Its upper border fuses laterally 
with the back of the postglenoid process, while medially it bounds the petro- 
tympanic fissure. The medial part of the lower border is thin and sharp; its lateral 
part splits to enclose the root of the styloid process, and is therefore named the 
vaginal process. The central portion of the tympanic part is thin, and in a consid- 
erable percentage of skulls is perforated by a hole, the foramen of Huschke. 

The external acoustic meatus is nearly 2 cm. long and is directed inward and 
slightly forward: at the same time it forms a slight curve, so that the floor of the 
canal is convex upward. In sagittal section it presents an oval or elliptical shape 
with the long axis directed downward and slightly backward. Its anterior wall 
and floor and the lower part of its posterior wall are formed by the tympanic 
part; the roof and upper part of the posterior wall by the squama. Its inner 
end is closed, in the recent state, by the tympanic membrane; the upper limit 
of its outer orifice is formed by the posterior root of the zygomatic process, imme- 
diately below which there is sometimes seen a small spine, the suprameatal spine, 
situated at the upper and posterior part of the orifice. 

Styloid Process (processus styloideus) . — The styloid process is slender, pointed, 
and of varying length; it projects downward and forward, from the under surface 
of the temporal bone. Its proximal part (tympanohyal) is ensheathed by the 
vaginal process of the tympanic portion, while its distal part (stylohyal) gives 
attachment to the stylohyoid and stylomandibular ligaments, and to the Stylo- 
glossus, Stylohyoideus, and Stylopharyngeus muscles. The stylohyoid ligament 
extends from the apex of the process to the lesser cornu of the hyoid bone, and 
in some instances is partially, in others completely, ossified. 

Structure.^ — The structure of the squama is like that of the other cranial bones: the mastoid 
portion is spongy, and the petrous portion dense and hard. 

Ossification. — The temporal bone is ossified from eight centers, exclusive of those for the internal 
ear and the tympanic ossicles, viz., one for the squama including the zygomatic process, one for 
10 



146 



OSTEOLOGY 



the tympanic part, four for the patrous and mastoid parts, and two for the styloid process. Just 
before the close of fetal life (Fig. 142) the temporal bone consists of three principal parts: 1. 
The squama is ossified in membrane from a single nucleus, which appears near the root of the 
zygomatic process about the second month. 2. The petromastoid part is developed from four 
centers, which make their appearance in the cartilaginous ear capsule about the fifth or sixth 
month. One (prodtic) appears in the neighborhood of the eminentia arcuata, spreads in front 
and above the internal acoustic meatus and extends to the apex of the bone; it forms part of the 



Septum canalis musculotubarii . 

Fenestra vestibuli 
Tympanic antrum, 



Sulcus tympanicus 




Bristle in facial 
canal 



Lateral wall of 
tympanic antrum 



Fig. 142. — The three principal parts of the tempora bone at birth. 1. Outer surface of petromastoid part. 
2. Outer surface of tympanic ring. 3. Inner surface of squama. 

cochlea, vestibule, superior semicircular canal, and medial wall of the tympanic cavity. A second 
{opisthotic) appears at the promontory on the medial wall of the tympanic cavity and surrounds 
the fenestra cochleae; it forms the floor of the tympanic cavity and vestibule, surrounds the carotid 
canal, invests the lateral and lower part of the cochlea, and spreads medially below the internal 
acoustic meatus. A third (pterotic) roofs in the tympanic cavity and antrum; while the fourth 



Squama 



Squama 



Petrosquamous 
suture 




Petrosquamous suture 
Eminentia arcuata 



Tympanic ring 



Petromastoid portion 

Fig. 143. — Temporal bone at birth. 
Outer aspect. 




Fig. 144. 



Fossa subarcuata 



Internal acoustic meatus 



-Temporal bone at birth. Inner 
aspect. 



(epiotic) appears near the posterior semicircular canal and extends to form the mastoid process 
(Vrolik), 3. The tympanic ring is an incomplete circle, in the concavity of which is a groove, 
the tympanic sulcus, for the attachment of the circumference of the tympanic membrane. This 
ring expands to form the tympanic part, and is ossified in membrane from a single center which 
appears about the third month. The styloid process is developed from the proximal part of the 
cartilage of the second branchial or hyoid arch by two centers: one for the proximal part, the 
tympanohyal, appears before birth; the other, comprising the rest of the process, is named the 



THE SPHENOID BONE 147 

slylohyal, and does not appear until after birth. The tympanic ring unites with the squama 
shortly before birth; the petromastoid part and squama join during the first year, and the tym- 
panohyal portion of the styloid process about the same time (Figs. 143, 144). The stylohyal 
does not unite with the rest of the bone until after puberty, and in some skulls never at all. 

The chief subsequent changes in the temporal bone apart from increase in size are: (1) The 
tympanic ring extends outward and backward to form the tympanic part. This extension does 
not, however, take place at an equal rate all around the circumference of the ring, but occurs most 
rapidly on its anterior and posterior portions, and these outgrowths meet and blend, and thus, 
for a time, there exists in the floor of the meatus a foramen, the foramen of Huschke; this foramen 
is usually closed about the fifth year, but may persist throughout Ufe. (2) The mandibular fossa 
is at first extremely shallow, and looks lateralward as well as downward; it becomes deeper and 
is ultimately directed downward. Its change in direction is accounted for as follows. The part 
of the squama which forms the fossa lies at first below the level of the zygomatic process. As, 
however, the base of the skull increases in width, this lower part of the squama is directed hori- 
zontally inward to contribute to the middle fossa of the skull, and its surfaces therefore come 
to look upward and downward; the attached portion of the zygomatic process also becomes 
everted, and projects like a shelf at right angles to the squama. (3) The mastoid portion is at 
first quite flat, and the stylomastoid foramen and rudimentary styloid process lie immediately 
behind the tympanic ring. With the development of the air cells the outer part of the mastoid 
portion grows downward and forward to form the mastoid process, and the styloid process and 
stylomastoid foramen now come to lie on the under surface. The descent of the foramen is 
necessarily accompanied by a corresponding lengthening of the facial canal. (4) The downward 
and forward growth of the mastoid process also pushes forward the tympanic part, so that the 
portion of it which formed the original floor of the meatus and contained the foramen of Huschke 
is ultimately found in the anterior wall. (5) The fossa subarcuata becomes filled up and almost 
obliterated. 

Articulations.— The temporal articulates with five bones : occipital, parietal, sphenoid, mandible 
and zygomatic. 

The Sphenoid Bone (Os Sphenoidale). 

The sphenoid bone is situated at the base of the skull in front of the temporals 
and basilar part of the occipital. It somewhat resembles a bat with its wings 
extended, and is divided into a median portion or body, two great and two small 
wings extending outward from the sides of the body, and two pterygoid processes 
which project from it below. 

Body {corpus si>henoidale) . — The body, more or less cubical in shape, is hollowed 
out in its interior to form two large cavities, the sphenoidal air sinuses, which are 
separated from each other by a septum. 

Surfaces. — The superior surface of the body (Fig. 145) presents in front a promi- 
nent spine, the ethmoidal spine, for articulation with the cribriform plate of the 
ethmoid; behind this is a smooth surface slightly raised in the middle line, and 
grooved on either side for the olfactory lobes of the brain. This surface is bounded 
behind by a ridge, which forms the anterior border of a narrow, transverse groove, 
the chiasmatic groove {optic groove), above and behind which lies the optic chiasma; 
the groove ends on either side in the optic foramen, which transmits the optic 
nerve and ophthalmic artery into the orbital cavity. Behind the chiasmatic 
groove is an elevation, the tuberculum sellae; and still more posteriorly, a deep 
depression, the sella turcica, the deepest part of which lodges the hypophysis 
cerebri and is known as the fossa hypophyseos. The anterior boundary of the 
sella turcica is completed by two small eminences, one on either side, called the 
middle clinoid processes, while the posterior boundary is formed by a square- 
shaped plate of bone, the dorsum sellae, ending at its superior angles in two tubercles, 
the posterior clinoid processes, the size and form of which vary considerably in 
different individuals. The posterior clinoid processes deepen the sella turcica, 
and give attachment to the tentorium cerebelli. On either side of the dorsum 
sells is a notch for the passage of the abducent nerve, and below the notch a sharp 
process, the petrosal process, which articulates with the apex of the petrous portion 
of the temporal bone, and forms the medial boundary of the foramen lacerum. 



148 



OSTEOLOGY 



Behind the dorsum sellse is a shallow depression, the clivus, which slopes obliquely 
backward, and is continuous with the groove on the basilar portion of the occipital 
bone; it supports the upper part of the pons. 



Middle Clinoid process 
Posterior Clinoid process 



Ethmoidal 

spine 

Groove for 
olfactoni 




Optic foramen 
Superior orbital 
fissu re 

Foramen rotund um 

Foramen Vesalii 

Foramen orale 

Foramen spinonum 



Spina annularis 



palatine 



Fig. 14o. — Sphenoid bone. Upper surface. 



The lateral surfaces of the body are united with the great wings and the medial 
pterygoid plates. Above the attachment of each great wing is a broad groove, 
curved something like the italic letter /; it lodges the internal carotid artery and 
the cavernous sinus, and is named the carotid groove. Along the posterior part 




Infratemporal 
crext 



Tensor vel 
palatini 



Medial pteryrjo 



Fig. 14G. — Sphenoid bone. .Vnterior and inferior surfaces. 



of the lateral margin of this groove, in the angle between the body and great wing, 
is a ridge of bone, called the lingula. 

The posterior surface, quadrilateral in form (Fig. 147), is joined, during infancy 
and adolescence, to the basilar part of the occipital bone by a plate of cartilage. 



THE SPHENOID BONE 



149 



Between the eighteenth and twenty-fifth years this becomes ossified, ossification 
commencing above and extending downward. 

The anterior surface of the body (Fig. 14()) presents, in the middle line, a vertical 
crest, the sphenoidal crest, which articulates with the perpendicular plate of the 
ethmoid, and forms part of the septum of the nose. On either side of the crest 
is an irregular opening leading into the corresponding sphenoidal air sinus. These 
sinuses are two large, irregular cavities hollowed out of the interior of the body 
of the bone, and separated from one another by a bony septum, which is commonly 
bent to one or the other side. They vary considerably in form and size,^ are 
seldom symmetrical, and are often partially subdivided by irregular bony lamina. 
Occasionally, they extend into the basilar part of the occipital nearly as far as the 
forameri magnum. They begin to be developed before birth, and are of a consid- 
erable size by the age of six. They are partially closed, in front and below, by two 
thin, curved plates of bone, the sphenoidal conchse (see page ]r)2), leaving in the 
articulated skull a round opening at the upper part of each sinus by which it com- 

Anlerior clinoid process 
Posterior clinoid process j Jsfoich jor abducent 




oramen rolundum 



f f\ «'i<fcw • Spina anguiaris 

Scaphoid fossa' IMUr^^ / / /Ml ( ^^terygoid canal 

Pterygoid fossa z:jMS^'m I I 1 111 -^^^ Lateral pteryuoid lamina 

Medial pterygoid lamina 

Hamulus 



Rostrum 
FiQ. 147. — Sphenoid bone. Upper and posterior surfaces. 

municates with the upper and back part of the nasal cavity and occasionally with 
the posterior ethmoidal air cells. The lateral margin of the anterior surface is 
serrated, and articulates with the lamina papyracea of the ethmoid, completing 
the posterior ethmoidal cells; the lower margin articulates with the orbital process 
of the palatine bone, and the upper with the orbital plate of the frontal bone. 

The inferior surface presents, in the middle line, a triangular spine, the sphenoidal 
rostrum, which is continuous with the sphenoidal crest on the anterior surface, 
and is received in a deep fissure between the ahe of the vomer. On either side of 
the rostrum is a projecting lamina, the vaginal process, directed medialward from 
the base of the medial pterygoid plate, with which it will be described. 

The Great Wings (alee inagncp). — The great wings, or ali-sphenoids, are two 
strong processes of bone, which arise from the sides of the body, and are curved 
upward, lateralward, and backward; the posterior part of each projects as a tri- 
angular process which fits into the angle between the squama and the petrous 



' Aldren Turner {op. cit.) gives the following a.-) their average measurements: vertical height, '/s inch: antero-posterior 
depth, '/s inch; transverse breadth, ?^ inch. 



150 OSTEOLOGY 

portion of the temporal and presents at its apex a downwardly directed process, 
the spina angularis {sphenoidal spine). 

Surfaces. — ^The superior or cerebral surface of each great wing (Fig. 145) forms 
part of the middle fossa of the skull; it is deeply concave, and presents depressions 
for the convolutions of the temporal lobe of the brain. At its anterior and medial 
part is a circular aperture, the foramen rotiindum, for the transmission of the maxil- 
lary nerve. Behind and lateral to this is the foramen ovale, for the transmission 
of the mandibular nerve, the accessory meningeal artery, and sometimes the 
lesser superficial petrosal nerve. ^ Medial to the foramen ovale, a small aperture, 
the foramen Vesalii, may occasionally be seen opposite the root of the pterygoid 
process; it opens below near the scaphoid fossa, and transmits a small vein from 
the cavernous sinus. Lastly, in the posterior angle, near to and in front of the spine, 
is a short canal, sometimes double, the foramen spinosum, which transmits the 
middle meningeal vessels and a recurrent branch from the mandibular nerve. 

The lateral surface (Fig. 146) is convex, and divided by a transverse ridge, the 
infratemporal crest, into two portions. The superior or temporal portion, convex 
from above downward, concave from before backward, forms a part of the tem- 
poral fossa, and gives attachment to the Temporalis; the inferior or infratemporal, 
smaller in size and concave, enters into the formation of the infratemporal fossa, 
and, together with the infratemporal crest, affords attachment to the Pterygoideus 
externus. It is pierced by the foramen ovale and foramen spinosum, and at its 
posterior part is the spina angularis, which is frequently grooved on its medial 
surface for the chorda tympani nerve. To the spina angularis are attached the 
sphenomandibular ligament and the Tensor veli palatini. Medial to the anterior 
extremity of the infratemporal crest is a triangular process which serves to increase 
the attachment of the Pterygoideus externus; extending downward and medialward 
from this process on to the front part of the lateral pterygoid plate is a ridge which 
forms the anterior limit of the infratemporal surface, and, in the articulated skull, 
the posterior boundary of the pterygomaxillary fissure. 

The orbital surface of the great wing (Fig. 146), smooth, and quadrilateral in 
shape, is directed forward and medialward and forms the posterior part of the 
lateral wall of the orbit. Its upper serrated edge articulates with the orbital plate 
of the frontal. Its inferior rounded border forms the postero-lateral boundary of 
the inferior orbital fissure. Its medial sharp margin forms the lower boundary 
of the superior orbital fissure and has projecting from about its center a little 
tubercle which gives attachment to the inferior head of the Rectus lateralis oculi; 
at the upper part of this margin is a notch for the transmission of a recurrent 
branch of the lacrimal artery. Its lateral margin is serrated and articulates with 
the zygomatic bone. Below the medial end of the superior orbital fissure is a 
grooved surface, which forms the posterior wall of the pterygopalatine fossa, 
and is pierced by the foramen rotundum. 

Margin (Fig. 145). — Commencing from behind, that portion of the circum- 
•ference of the great wing which extends from the body to the spine is irregular. 
Its medial half forms the anterior boundary of the foramen lacerum, and presents 
the posterior aperture of the pterygoid canal for the passage of the correspond- 
ing nerve and artery. Its lateral half articulates, by njeans of a synchondrosis, 
with the petrous portion of the temporal, and between the two bones on the 
under surface of the skull, is a furrow, the sulcus tubse, for the lodgement of the 
cartilaginous part of the auditory tube. In front of the spine the circumference 
presents a concave, serrated edge, bevelled at the expense of the inner table below, 
and of the outer table above, for articulation with the temporal squama. At 
the tip of the great wing is a triangular portion, bevelled at the expense of the 

* The lesser superficial petrosal nerve sometimes passes through a special canal (canaliculus innominatus of Arnold) 
situated medial to the foramen spinosum. 



THE SPHENOID BONE 151 

internal surface, for articulation with the sphenoidal angle of the parietal bone; 
this region is named the pterion. Medial to this is a triangular, serrated surface, 
for articulation with the frontal bone; this surface is continuous medially with 
the sharp edge, which forms the lower boundary of the superior orbital fissure, 
and laterally with the serrated margin for articulation with the zygomatic bone. 

The Small Wings (a/cp parvce). —The small wings or orbito-sphenoids are two 
thin triangular plates, which arise from the upper and anterior parts of the body, 
and, projecting lateralward, end in sharp points (Fig. 145). 

Surfaces.— The superior surface of each is flat, and supports part of the frontal 
lobe of the brain. The inferior surface forms the back part of the roof of the orbit, 
and the upper boundary of the superior orbital fissure. This fissure is of a triangular 
form, and leads from the cavity of the cranium into that of the orbit: it is bounded 
mediaUy by the body; above, by the small wing; beloiv, by the medial margin of 
the orbital surface of the great wing; and is completed laterally by the frontal 
bone. It transmits the oculomotor, trochlear, and abducent nerves, the three 
branches of the ophthalmic division of the trigeminal nerve, some filaments from 
the cavernous plexus of the sympathetic, the orbital branch of the middle menin- 
^ geal artery, a recurrent branch from the lacrimal artery to the dura mater, and the 
* ophthalmic vein. 

Borders. — The anterior border is serrated for articulation with the frontal bone. 
The posterior border, smooth and rounded, is received into the lateral fissure of 
the brain; the medial end of this border forms the anterior clinoid process, which 
gives attachment to the tentorium cerebelli; it is sometimes joined to the middle 
clinoid process by a spicule of bone, and when this occurs the termination of the 
groove for the internal carotid artery is converted into a foramen (carotico-clinoid). 
The small wing is connected to the body by two roots, the upper thin and flat, 
the lower thick and triangular; between the two roots is the optic foramen, for the 
transmission of the optic nerve and ophthalmic artery. 

Pterygoid Processes (processus pterygoidei). — The pterygoid processes, one on 
either side, descend perpendicularly from the regions where the body and great 
wings unite. Each process consists of a medial and a lateral plate, the upper parts 
of which are fused anteriorly; a vertical sulcus, the pterygopalatine groove, descends 
on the front of the line of fusion. The plates are separated below by an angular 
cleft, the pterygoid fissure, the margins of which are rough for articulation with 
the pyramidal process of the palatine bone. The two plates diverge behind and 
enclose between them a V-shaped fossa, the pterygoid fossa, which contains the 
Pterygoideus internus and Tensor veli palatini. Above this fossa is a small, oval, 
shallow depression, the scaphoid fossa, which gives origin to the Tensor veli palatini. 
The anterior surface of the pterygoid process is broad and triangular near its 
root, where it forms the posterior wall of the pterygopalatine fossa and presents 
the anterior orifice of the pterygoid canal. 

Lateral Pterygoid Plate. — The lateral pterygoid plate is broad, thin, and everted; 
its lateral surface forms part of the medial wall of the infratemporal fossa, and 
gives attachment to the Pterygoideus externus; its medial surface forms part of 
the pterygoid fossa, and gives attachment to the Pterygoideus internus. 

Medial Pterygoid Plate. — The medial pterygoid plate is narrower and longer 
than the lateral ; it curves lateralward at its lower extremity into a hook-like pro- 
cess, the pterygoid hamulus, around which the tendon of the Tensor veli palatini 
glides. The lateral surface of this plate forms part of the pterygoid fossa, the 
medial surface constitutes the lateral boundary of the choana or posterior aperture 
of the corresponding nasal cavity. Superiorly the medial plate is prolonged on to 
the under surface of the body as a thin lamina, named the vaginal process, which 
articulates in front with the sphenoidal process of the palatine and behind this 
with the ala of the vomer. The angular prominence between the posterior margin 



152 



OSTEOLOGY 



of the vaginal process and the medial border of the scaphoid fossa is named the 
pterygoid tubercle, and immediately above this is the posterior opening of the 
pterygoid canal. On the under surface of the vaginal process is a furrow, which 
is converted into a canal by the sphenoidal process of the palatine bone, for the 
transmission of the pharyngeal branch of the internal maxillary artery and the 
pharyngeal nerve from the sphenopalatine ganglion. The pharyngeal aponeurosis 
is attached to the entire length of the posterior edge of the medial plate, and the 
Constrictor pharyngis superior takes origin from its lower third. Projecting 
backward from near the middle of the posterior edge of this plate is an angular 
process, the processus tubarius, which supports the pharyngeal end of the auditory 
tube. The anterior margin of the plate articulates with the posterior border of 
the vertical part of the palatine bone. 

The Sphenoidal Conchse {conchce sphenoidales; sphenoidal iurbiiiated processes). 
— The sphenoidal concha^ are two thin, curved plates, situated at the anterior 
and lower part of the body of the sphenoid. An aperture of variable size exists 
in the anterior wall of each, and through this the sphenoidal sinus opens into the 
nasal cavity. Each is irregular in form, and tapers to a point behind, being broader 
and thinner in front. Its upper surface is concave, and looks toward the cavity 
of the sinus; its under surface is convex, and forms part of the roof of the corre- 
sponding nasal cavity. Each bone articulates in front with the ethmoid, laterally 
with the palatine; its pointed posterior extremity is placed above the vomer, 
and is received between the root of the pterygoid process laterally and the rostrum 
of the sphenoid medially. A small portion of the sphenoidal concha sometimes 
enters into the formation of the medial wall of the orbit, between the lamina 
papyracea of the ethmoid in front, the orbital plate of the palatine below, and the 
frontal bone above. 




Ossification. — Until the seventh or eighth month of fetal life the body of the sphenoid consists 
of two parts, viz., one in front of the tubercuhim scUae, the prespheuoid, with which the small 
wings are continuous; the other, comprising the sella turcica and dorsum sella^, the postsphenoid, 

with which are associated the great 
wings, and pterygoid processes. The 
greater part of the bone is ossified in 
cartilage. There are fourteen centers 
in all, six for the presphenoiil and eight 
for the postsphenoid. 

Presphenoid. — About the ninth week 
of fetal life an ossific center appears for 
each of the small wings (orbit osphenoids) 
just lateral to the oi)tic foramen; shortly 
afterward two nuclei appear in the pre- 
sphenoid part of the body. The sphe- 
noidal concha^ are each developed from 
a center which makes its appearance about the fifth month ;i at birth they consist of small 
triangular lamina^, and it is not until the third year that they become hollowed out and cone- 
shaped; about the fourth year they fuse with the labyrinths of tlie ethmoid, and between the 
ninth and twelfth years they unite with the sphenoid. 

Postsphenoid. — The first ossific nuclei are those for the great wings (ali-sphenoids)=. ( )ne makes 
its appearance in each wing between the foramen rotundum and foramen ovale about the eighth 
week. The orbital plate and that part of the sjihenoid which is found in the temporal fossa, as 
well as the lateral pterygoid plate, are ossified in membrane (Fawcett)^ Soon after, the centers 
for the postsphenoid part of the body appear, one on either side of the sella turcica, and become 
blended together about the middle of fetal life. Each medial pterygoid plate (.with the exception 
of its hamulus) is ossified in membrane, and its center probably appears about the ninth or tenth 
week; the hamulus becomes chondrified during the third month, and almost at once imdergoes 



Fig. 148. — Sphenoid bone at birth. Posterior aspect. 



' According to Cleland, each sphenoidal concha is ossified from four centers. 

2 Mall. Am. .lour. Anat., 1906, states that the pterjgoid center appears first in an embryo fifty-seven days old. 

s Journal of Anatomy and Physiology, 1910, vol. xliv. 



THE ETHMOID BONE 



153 



ossification (Fawcett). The medial joins the lateral pterygoid plate about the sixth month. 
About the fourth month a center appears for each lingula and speedily joins the rest of the bone. 
The presphenoid is united to the postsphenoid about the eighth month, and at birth the bone 
IS in three pieces (Fig. 148) : a central, consisting of the body and small wings, and two lateral, 
each compnsmg a great wing and ptery-goid. process. In the first vear after birth the great wings 
and body unite, and the small wings extend inward above the anterior part of the body, and, 
meeting with each other in the middle hne, form an elevated smooth surface, termed ihejugum 
sphenoidale. By the twenty-fifth year the sphenoid and occipital arc completely fused. Between 
the pre- and postsphenoid there are occasionally seen the remains of a canal, the canalis cranio- 
pharyngeus, through which, in early fetal life, the hypophyseal diverticulum of the buccal ecto- 
derm IS transmitted. 

The sphenoidal sinuses are present as minute cavities at the time of birth (Onodi), but do not 
attain their full size until after puberty. 

Intrinsic Ligaments of the Sphenoid.— The more important of these are: the pierygospinous, 
stretching between the spina angularis and the lateral pterj^goid plate (see cervical fascia); the 
tnterchnoid, a fibrous process joining the anterior to the posterior clinoid process; and the 
caroticoclinoid, connecting the anterior to the middle cUnoid process. These ligaments occa- 
sionally ossify. 

Articulations.— The sphenoid articulates with twelve bones: four single, the vomer, ethmoid, 
frontal, and occipital; and four paired, the parietal, temporal, zygomatic, and palatine.^ 



The Ethmoid Bone fOs Ethmoidale). 

The ethmoid bone i.s exceedingly light and spongy, and cubical in shape; it 
IS situated at the anterior part of the base of the cranium, between the two orbits, 
at the roof of the nose, and contributes to each of these cavities. It consists of 
four parts: a horizontal or cribriform plate, forming part of the base of the cranium; 
a perpendicular plate, constituting part of the nasal septum; and two lateral masses 
or labyrinths. 

Cribiform Plate {lamina cribrosa; horizontal lamina).— The cribriform plate 
(Fig. 149) is received into the ethmoidal notch of the frontal bone and roofs in 
the nasal cavities. Projecting upward from the middle line of this plate is a thick, 
smooth, triangular process, the crista galli, so called from its resemblance to a 
cock's comb. The long thin posterior border of the crista galli serves for the 
attachment of the falx cerebri. 
Its anterior border, short and 
thick, articulates with the frontal 
bone, and presents two small pro- 
jecting alae, which are received 
into corresponding depressions in 
the frontal bone and complete 
the foramen cecum. Its sides are 
smooth, and sometimes bulging 
from the presence of a small air 
sinus in the interior. On either 
side of the crista galli, the cribri- 
form plate is narrow and deeply 
grooved ; it supports the olfactory 
bulb and is perforated by fora- 
mina for the passage of the olfac- 
tory nerves. The foramina in the 
middle of the groove are small 
and transmit the nerves to the 

roof of the nasal cavity; those at the medial and lateral parts of the groove are 
larger — the former transmit the nerves to the upper part of the nasal septum, 
the latter those to the superior nasal concha. At the front part of the cribriform 

' Anatomischer Anzeiger. March. 1905. 
It also sometimes articulates with the tuberosity of the maxilla (see page 159). 



Perpendicular plate 
Ala 



Crista galli 




Cribriform plain 

Anterior ethmoidal 
groove 



Posterior ethmoidal 
groove 



Fig. 149. — tlhiuoid bone from above. 



154 



OSTEOLOGY 



plate, on either side of the crista galh, is a small fissure which is occupied by a 
process of dura mater. Lateral to this fissure is a notch or foramen which trans- 



mits the nasociliary nerve; from this notch 
anterior ethmoidal foramen. 



a groove extends backward to the 



^thEthmo. 




Fig. 150. — Perpendicular plate of ethmoid. Shown by removing the right labyrinth. 



Perpendicular Plate (laviina perpendmdaris; vertical plate). — The perpendicular 
plate (Figs. 150, 151) is a thin, flattened lamina, polygonal in form, which descends 
from the under surface of the cribriform plate, and assists in forming the septum 
of the nose; it is generally deflected a little to one or other side. The anterior border 
articulates with the spine of the frontal bone and the crest of the nasal bones. 
The posterior border articulates by its upper half with the sphenoidal crest, by its 
lower with the vomer. The inferior border is thicker than the posterior, and serves 
for the attachment of the septal cartilage of the nose. The surfaces of the plate 
are smooth, except above, where numerous grooves and canals are seen; these 
lead from the medial foramina on the cribriform plate and lodge filaments of the 
olfactory nerves. 

The Labyrinth or Lateral Mass {labyrinthus ethmoidalis) consists of a number 
of thin-walled cellular cavities, the ethmoidal cells, arranged in three groups, 

anterior, middle, and posterior, and inter- 
posed between two vertical plates of bone ; 
the lateral plate forms part of the orbit, 
the medial, part of the corresponding 
nasal cavity. In the disarticulated bone 
many of these cells are opened into, but 
when the bones are articulated, they are 
closed in at every part, except where 
they open into the nasal cavity. 

Surfaces. — The upper surface of the laby- 
rinth (Fig. 149) presents a number of 
half-broken cells, the walls of which are 
completed, in the articulated skull, by 
the edges of the ethmoidal notch of the 
frontal bone. Crossing this surface are 
two grooves, converted into canals by articulation with the frontal; they are the 
anterior and posterior ethmoidal canals, and open on the inner wall of the orbit. 
The posterior surface presents large irregular cellular cavities, which are closed in 




Fig. 151.- 



Crista gain 



— Labyrinth 

Superior nasal 

concha 
Superior meatus 

Uncinate process 

Middle nasal concha 
Perpendicular plate 
Ethmoid bone from behind. 



THE ETHMOID BONE 



155 



by articulation with the sphenoidal concha and orbital process of the palatine. 
The lateral surface (Fig. 152) is formed of a thin, smooth, oblong plate, the lamina 
papyracea {os planum), which covers in the middle and posterior ethmoidal cells 




Ethmoidal 
cells 



Per'pendicular 

plate 



Uncinate process 



Fig. 152. — Ethmoid bone from the right side. 



and forms a large part of the medial wall of the orbit; it articulates above with 
the orbital plate of the frontal bone, below with the maxilla and orbital process 
of the palatine, in front with the lacrimal, and behind with the sphenoid. 

In front of the lamina papyracea are some broken air cells which are overlapped 
and completed by the lacrimal bone and the frontal process of the maxilla. A 



Frontal sinus 



Crista galli 



Sella turcica 



Uncinate 

process of 

ethmoid 




ngs into 
maxillary simis 
Medial pterygoid plate 

Hamulus 



Fio. 153. — Lateral wall of nasal cavity, showing ethmoid bone in position. 



curved lamina, the uncinate process, projects downward and backward from this 
part of the labyrinth; it forms a small part of the medial wall of the maxillary 
sinus, and articulates with the ethmoidal process of the inferior nasal concha. 



156 OSTEOLOGY 

The medial surface of the labyrinth (Fig. 153) forms part of the lateral wall 
of the corresponding nasal cavity. It consists of a thin lamella, which descends 
from the under surface of the cribriform plate, and ends below in a free, convoluted 
margin, the middle nasal concha. It is rough, and marked above by numerous 
grooves, directed nearly vertically downward from the cribriform plate; they 
lodge branches of the olfactory nerves, which are distributed to the mucous mem- 
brane covering the superior nasal concha. The back part of the surface is sub- 
divided by a narrow oblique fissure, the superior meatus of the nose, bounded above 
by a thin, curved plate, the superior nasal concha; the posterior ethmoidal cells 
open into this meatus. Below, and in front of the superior meatus, is the convex 
surface of the middle nasal concha; it extends along the whole length of the medial 
surface of the labyrinth, and its lower margin is free and thick. The lateral surface 
of the middle concha is concave, and assists in forming the middle meatus of the 
nose. The middle ethmoidal cells open into the central part of this meatus, and a 
sinuous passage, termed the infundibulum, extends upward and forward through 
the labyrinth and communicates with the anterior ethmoidal cells, and in about 
50 per cent, of skulls is continued upward as the frontonasal duct into the frontal 
sinus. 

Ossification. — The ethmoid is ossified in the cartilage of the nasal capsule by three centers: 
one for the perpendicular plate, and one for each labyrinth. 

The labjTinths are first developed, ossific granules making their appearance in the region of 
the lamina papyracea between the fourth and fifth months of fetal life, and extending into the 
concha^. At birth, the bone consists of the two labyrinths, which are small and ill-developed. 
During the first year after birth, the perpendicular plate and crista galli begin to ossify from a 
single center, and are joined to the labyrinths about the beginning of the second year. The 
cribriform plate is ossified partly from the perpendicular plate and partly from the labyrinths. 
The development of the ethmoidal cells begins during fetal life. 

Articulations. — The ethmoid articulates with fifteen bones: four of the cranium — the frontal, 
the sphenoid, and the two sphenoidal conchse; and eleven of the face — -the two nasals, two maxilla), 
two lacrimals, two palatines, two inferior nasal conchie, and the vomer. 

Sutural or Wormian' Bones. — In addition to the usual centers of ossification of the cranium, 
others may occur in the course of the sutures, giving rise to irregular, isolated bones, termed 
sutural or Wormian bones. They occur most frequently in the course of the lambdoidal suture, 
but are occasionally seen at the fontanelles, especially the posterior. One, the pterion ossicle, 
sometimes exists between the sphenoidal angle of the parietal and the great wing of the sphenoid. 
They have a tendency to be more or less symmetrical on the two sides of the skull, and vary 
much in size. Their number is generally limited to two or three; but more than a hundred have 
been found in the skull of an adult hydrocephalic subject. 



THE FACIAL BONES (OSS A FACIEI). 

The Nasal Bones (Ossa Nasalia). 

The nasal bones are two small oblong bones, varying in size and form in different 
individuals; they are placed side by side at the middle and upper part of the face, 
and form, by their junction, "the bridge" of the nose (Fig. 190). Each has two 
surfaces and four borders. 

Surfaces. — The outer surface (Fig. 155) is concavoconvex from above downward, 
convex from side to side; it is covered by the Procerus and Compressor naris, and 
perforated about its center by a foramen, for the transmission of a small vein. 
The inner surface (F'ig. 150) is concave from side to side, and is traversed from above 
downward, by a groove for the passage of a branch of the nasociliary nerve. 

Borders. — The superior border is narrow, thick, and serrated for articulation with 
the nasal notch of the frontal bone. The inferior border is thin, and gives attach- 

' Ole Worm, Professor of Anatomy at Copenhagen, 1624-1639, was erroneously supposed to have given the first 
detailed description of these bones. 



THE MAXILLA 



157 



ment to the lateral cartilage of the nose; near its middle is a notch which marks 
the end of the groove just referred to. The lateral border is serrated, bevelled 
at the expense of the inner surface above, and of the outer below, to articulate 
with the frontal process of the maxilla. The medial border, thicker above than 



Fossa for lacrimal sac 



Infraorbital 
foramen 




Fig. 154. — Articulation of nasal and lacrimal bones with maxilla. 

below, articulates with its fellow of the opposite side, and is prolonged behind into 
a vertical crest, which forms part of the nasal septum: this crest articulates, from 
above downward, with the spine of the frontal, the perpendicular plate of the 
ethmoid, and the septal cartilage of the nose. 



Foramen 
'or vein 



fiit/i 





Fig. 155. — Right nasal bone. Outer surface. 



Groove. 
Fig. 156. — Right nasal bone. Inner surface. 



Ossification. — Each bone is ossified from one center, which appears at the beginning of the 
third month of fetal life in the membrane overlying the front part of the cartilaginous nasal 
capsule. 

Articulations. — The nasal articulates with four bones: two of the cranium, the frontal and 
ethmoid, and two of the face, the opposite nasal and the maxilla. 



The Maxillae (Upper Jaw). 

The maxillae are the largest bones of the face, excepting the mandible, and 
form, by their union, the whole of the upper jaw. Each assists in forming the 



158 



OSTEOLOGY 



boundaries of three cavities, viz., the roof of the mouth, the floor and lateral 
wall of the nose and the floor of the orbit; it also enters into the formation of two 
fossae, the infratemporal and pterygopalatine, and two fissures, the inferior orbital 
and pterygomaxillary. 

Each bone consists of a body and four processes — zygomatic, frontal, alveolar, 
and palatine. 

The Body (corpus maxillor). — The body is somewhat pyramidal in shape, and 
contains a large cavity, the maxillary sinus (antrum of HigJunore). It has four 
surfaces — an anterior, a posterior or infratemporal, a superior or orbital, and a 
medial or nasal. 

Surfaces. — The anterior surface (Fig, 157) is directed forward and lateralward. 
It presents at its lower part a series of eminences corresponding to the positions 
of the roots of the teeth. Just above those of the incisor teeth is a depression, 
the incisive fossa, which gives origin to the Depressor a\-x nasi; to the alveolar 
border below the fossa is attached a slip of the Orbicularis oris; above and a little 



Med. palp. lig.~r^l 



I* ^Lacrimal tubercle 



DILATATOR NARIS POSTERIOR 



Incisive fossa 




"tu ^Alveclar canals 



Maxillary tuberosity 



Fig. 157. — Left masilla. Outer surface. 

lateral to it, the Xasalis arises. Lateral to the incisive fossa is another depression, 
the canine fossa; it is larger and deeper than the incisive fossa, and is separated 
from it by a vertical ridge, the canine eminence, corresponding to the socket of 
the canine tooth; the canine fossa gives origin to the Caninus. Above the fossa 
is the infraorbital foramen, the end of the infraorbital canal ; it transmits the infra- 
orbital vessels and nerve. Above the foramen is the margin of the orbit, which 
affords attachment to part of the Quadratus labii superioris. ^Medially, the anterior 
surface is limited by a deep concavity, the nasal notch, the margin of which gives 
attachment to the Dilatator naris posterior and ends below in a pointed process, 
which with its fellow of the opposite side forms the anterior nasal spine. 

The infratemporal surface (Fig. 157) is convex, directed backward and lateral- 
ward, and forms part of the infratemporal fossa. It is separated from the anterior 
surface by the zygomatic process and by a strong ridge, extending upward from 
the socket of the first molar tooth. It is pierced about its center by the apertures 
of the alveolar canals, which transmit the posterior superior alveolar vessels and 
nerves. At the lower part of this surface is a rounded eminence, the maxillary 



THE MAXILLA 



159 



tuberosity, especially prominent after the growth of the wisdom tooth; it is rough 
on its lateral side for articulation with the pyramidal process of the palatine bone 
and in some cases articulates with the lateral pterygoid plate of the sphenoid. 
It gives origin to a few fibers of the Pterygoideus internus. Immediately above 
this is a smooth surface, which forms the anterior boundary of the pterygopalatine 
fossa, and presents a groove, for the maxillary nerve; this groove is directed lateral- 
ward and slightly upward, and is continuous with the infraorbital groove on the 
orbital surface. 

The orbital surface (Fig. 157) is smooth and triangular, and forms the greater 
part of the floor of the orbit. It is bounded medially by an irregular margin which 
in front presents a notch, the lacrimal notch; behind this notch the margin articu- 
lates with the lacrimal, the lamina papyracea of the ethmoid and the orbital process 
of the palatine. It is bounded behind by a smooth rounded edge which forms 
the anterior margin of the inferior orbital fissure, and sometimes articulates at 
its lateral extremity with the orbital surface of the great wing of the sphenoid. 



With frontal 



Bones partially closing orifice of sinus 
marked in red 



Ethmoid- 
Inferior nasal concha — -^^^V 
Palati}ie 




ith nasal bone 



Ani. TMsal spine 



Bristle passed 
through incisive 
canal 



Fig. 158. — Left maxilla. Nasal surface. 



It is limited in front by part of the circumference of the orbit, which is continuous 
medially with the frontal process, and laterally with the zyogmatic process. Near 
the middle of the posterior part of the orbital surface is the infraorbital groove, 
for the passage of the infraorbital vessels and nerve. The groove begins at the 
middle of the posterior border, where it is continuous with that near the upper 
edge of the infratemporal surface, and, passing forward, ends in a canal, which 
subdi^•ides into two branches. One of the canals, the infraorbital canal, opens 
just below the margin of the orbit; the other, wdiich is smaller, runs downward in 
the substance of the anterior wall of the maxillary sinus, and transmits the anterior 
superior alveolar vessels and nerve to the front teeth of the maxilla. From the 
back part of the infraorbital canal, a second small canal is sometimes given off; it 
runs downward in the lateral wall of the sinus, and con\'eys the middle alveolar 
nerve to the premolar teeth. At the medial and forepart of the orbital surface, 
just lateral to the lacrimal groove, is a depression, which gives origin to the Obliquus 
oculi inferior. 



160 



OSTEOLOGY 



The nasal surface (Fig. 158) presents a large, irregular opening leading into the 
maxillary sinus. At the upper border of this aperture are some broken air cells, 
which, in the articulated skull, are closed in by the ethmoid and lacrimal bones. 
Below the aperture is a smooth concavity which forms part of the inferior meatus 
of the nasal cavity, and behind it is a rough surface for articulation with the per- 
pendicular part of the palatine bone; this surface is traversed by a groove, com- 
mencing near the middle of the posterior border and running obliquely downward 
and forward; the groove is converted into a canal, the pterygopalatine canal, by the 
palatine bone. In front of the opening of the sinus is a deep groove, the lacrimal 
groove, which is converted into the nasolacrimal canal, by the lacrimal bone and 
inferior nasal concha; this canal opens into the inferior meatus of the nose and 
transmits the nasolacrimal duct. INlore anteriorly is an oblique ridge, the conchal 
crest, for articulation with the inferior nasal concha. The shallow concavity above 
this ridge forms part of the atrium of the middle meatus of the nose, and that 
below it, part of the inferior meatus. 



Anterior 
ethmoidal foramen 



Posterior ethmoidal foramen 
Orbital process of •palatine 
Oplic foiamen 

Sphenopalatine foramen 

SeUa turcica 
Probe m foramen rotundum 



Fossa for 

lacrimal sac 

Uncinate process 
of etinnoid 
Openings of 
maxillary sinus 
Inferior nasal 
concha 




Probe in pterygoid canal 
/ Probe in pterygopalatiiie canal 

/^Palatine bone 

\^ Lateral pterygoid plate 



Pyramidal process cf palatine 



Fig. 1o9. — Left maxillary sinus opened from the exterior. 



The Maxillary Sinus or Antrum of Highmore (simis maxillaris) . — The maxillary 
sinus is a large pyramidal cavity, within the body of the maxilla: its apex, directed 
lateralward, is formed by the zygomatic process; its base, directed medialward, 
by the lateral wall of the nose. Its walls are everywhere exceedingly thin, and 
correspond to the nasal orbital, anterior, and infratemporal surfaces of the body 
of the bone. Its nasal wall, or base, presents, in the disarticulated bone, a large, 
irregular aperture, communicating with the nasal cavity. In the articulated 
skull this aperture is much reduced in size by the following bones: the uncinate 
process of the ethmoid above, the ethmoidal process of the inferior nasal concha 
below, the vertical part of the palatine behind, and a small part of the lacrimal 
above and in front (Figs. 158, 159) ; the sinus communicates with the middle meatus 



THE MAXILLA 161 

of the nose, generally by two small apertures left between the above-mentioned 
bones. In the fresh state, usually only one small opening exists, near the upper 
part of the cavity; the other is closed by mucous membrane. On the posterior 
wall are the alveolar canals, transmitting the posterior superior alveolar vessels 
and nerves to the molar teeth. The floor is formed by the alveolar process of the 
maxilla, and, if the sinus be of an average size, is on a level with the floor of 
the nose; if the sinus be large it reaches below this level. 

Projecting into the floor of the antrum are several conical processes, correspond- 
ing to the roots of the first and second molar teeth ;i in some cases the floor is 
perforated by the fangs of the teeth. The infraorbital canal usually projects into 
the cavity as a well-marked ridge extending from the roof to the anterior wall; 
additional ridges are sometimes seen in the posterior wall of the cavity, and 
are caused by the alveolar canals. The size of the cavity varies in different skulls, 
and even on the two sides of the same skull. ^ 

The Zygomatic Process {processus zygomaticus; malar process). — The zygomatic 
process is a rough triangular eminence, situated at the angle of separation of the 
anterior, zygomatic, and orbital surfaces. In front it forms part of the anterior 
surface; beJmid, it is concave, and forms part of the infratemporal fossa; above, 
it is rough and serrated for articulation wdth the zygomatic bone; while below, 
it presents the prominent arched border which marks the division between the 
anterior and infratemporal surfaces. 

The Frontal Process ('processus frontalis; nasal process). — The frontal process 
is a strong plate, which projects upward, medialward, and backward, by the side 
of the nose, forming part of its lateral boundary. Its lateral surface is smooth, 
continuous with the anterior surface of the body, and gives attachment to the 
Quadratus labii superioris, the Orbicularis oculi, and the medial palpebral ligament. 
Its medial surface forms part of the lateral wall of the nasal cavity; at its upper 
part is a rough, uneven area, which articulates with the ethmoid, closing in the 
anterior ethmoidal cells; below this is an oblique ridge, the ethmoidal crest, the 
posterior end of which articulates with the middle nasal concha, while the anterior 
part is termed the agger nasi; the crest forms the upper limit of the atrium of the 
middle meatus. The upper border articulates with the frontal bone and the anterior 
with the nasal; the posterior border is thick, and hollowed into a groove, which is 
continuous below with the lacrimal groove on the nasal surface of the body: by 
the articulation of the medial margin of the groove with the anterior border of 
the lacrimal a corresponding groove on the lacrimal is brought into continuity, 
and together they form the lacrimal fossa for the lodgement of the lacrimal sac. 
The lateral margin of the groove is named the anterior lacrimal crest, and is con- 
tinuous below with the orbital margin; at its junction with the orbital surface is 
a small tubercle, the lacrimal tubercle, which serves as a guide to the position of 
the lacrimal sac. 

The Alveolar Process {processus alveolaris). — The alveolar process is the thickest 
and most spong}' part of the bone. It is broader behind than in front, and exca- 
vated into deep cavities for the reception of the teeth. These cavities are eight 
in number, and vary in size and depth according to the teeth they contain. That 
for the canine tooth is the deepest; those for the molars are the widest, and are 
subdivided into minor cavities by septa; those for the incisors are single, but 
deep and narrow. The Buccinator arises from the outer surface of this process, 
as far forward as the first molar tooth. When the maxillae are articulated with each 
other, their alveolar processes together form the alveolar arch; the center of the 
anterior margin of this arch is named the alveolar point. 

1 The number of teeth whose roots are in relation with the floor of the antrum is variable. The sinus "may extend 
so as to be in relation to all the teeth of the true maxilla, from the canine to the dens aapicnlicc. " (Salter.) 

2 Aldren Turner (op. cit.) gives the following measurements as those of an average sized sinus: vertical height 
opposite first molar tooth, 1}^ inch; transverse breadth, 1 inch; and antero-posterior depth, \]4 inch. 

11 



162 



OSTEOLOGY 



The Palatine Process (processus palatiniis; palatal process). — ^The palatine 
process, thick and strong, is horizontal and projects mediahvard from the nasal 
surface of the bone. It forms a considerable part of the floor of the nose and the 
roof of the mouth and is much thicker in front than behind. Its inferior surface 
(Fig. 160) is concave, rough and uneven, and forms, with the palatine process of 
the opposite bone, the anterior three-fourths of the hard plate. It is perforated 
by numerous foramina for the passage of the nutrient vessels; is channelled at the 
back part of its lateral border by a groove, sometimes a canal, for the transmission 
of the descending palatine vessels and the anterior palatine nerve from the spheno- 
palatine ganglion; and presents little depressions for the lodgement of the palatine 
glands. When the two maxillse are articulated, a funnel-shaped opening, the 
incisive foramen, is seen in the middle line, immediately behind the incisor teeth. 
In this opening the orifices of two lateral canals are visible; they are named the 



Incisive canals 



Incisive foramen 



Foramina of Scarpa 




Palatine process of mnzilla ^ Greater palatine foramen 

Horizontal plate of palatine bone Lesser palatine foramina 

Fig. 160. — The bony palate and alveolar arch. 

incisive canals or foramina of Stenson; through each of them passes the terminal 
branch of the descending palatine artery and the nasopalatine nerve. Occasionally 
,two additional canals are present in the middle line; they are termed the foramina 
of Scarpa, and when present transmit the nasopalatine nerves, the left passing 
through the anterior, and the right through the posterior canal. On the under 
surface of the palatine process, a delicate linear suture, well seen in young skulls, 
mav sometimes be noticed extending lateralward and forward on either side from 
the incisive foramen to the interval between the lateral incisor and the canine tooth. 
The small part in front of this suture constitutes the premaxilla {os incisimm), 
which in most vertebrates forms an independent bone ; it includes the whole thick- 
ness of the alveolus, the corresponding part of the floor of the nose and the anterior 
nasal spine, and contains the sockets of the incisor teeth. The upper surface of 
the palatine process is concave from side to side, smooth, and forms the greater 
part of the floor of the nasal cavity. It presents, close to its medial margin, the 



THE LACRIMAL BONE 



163 



upper orifice of the incisive canal. The lateral border of the process is incorporated 
with the rest of the bone. The medial border is thicker in front than behind, and 
is raised above into a ridge, the nasal crest, which, with the corresponding ridge 
of the opposite bone, forms a groove for the reception of the vomer. The front 
part of this ridge rises to a considerable height, and is named the incisor crest; 
it is prolonged forward into a sharp process, which forms, together with a similar 
process of the opposite bone, the anterior nasal spine. The 'posterior border is ser- 
rated for articulation with the horizontal part of the palatine bone. 

Ossification. — The maxilla is ossified in membrane. Mall* and Fawcett^ maintain that it is 
ossified from tiro centers only, one for the maxilla proper and one for the premaxilla. These 
centers appear during the sixth week of fetal life and unite in the beginning of the third month, 
but the suture between the two portions persists on the palate until nearly middle life. Mall 
states that the frontal process is developed from both centers. The maxillary sinus appears as 
a shallow groove on the nasal surface of the bone about the fourth month of fetal life, but does 
not reach its full size until after the second dentition. The maxilla was formerly described as 
ossifying from six centers, viz., one, the orbitonasal, forms that portion of the body of the bone 
which lies medial to the infraorbital canal, including the medial part of the floor of the orbit and 
the lateral wall of the nasal cavity; a second, the zygomatic, gives origin to the portion which lies 
lateral to the infraorbital canal, including the zj-gomatic process; from a third, the palatine, is 
developed the palatine process posterior to the incisive canal together with the adjoining part 
of the nasal wall; a fourth, the premaxillary, forms the incisive bone which carries the incisor 





Fig. 161. — Anterior surface of maxilla at birth. 



Fig. 162. — Inferior surface of maxilla at birth. 



teeth and corresponds to the premaxilla of the lower vertebrates;' a fifth, the nasal, gives rise to 
the frontal process and the portion above the canine tooth; and a sixth, the infravomerine, Ues 
between the palatine and premaxillary centers and beneath the vomer; this center, together with 
the corresponding center of the opposite bone, separates the incisive canals from each other. 

Articulations. — The maxilla articulates with nine bones: two of the cranium, the frontal and 
ethmoid, and seven of the face, viz., the nasal, zygomatic, lacrimal, inferior nasal concha, palatine, 
vomer, and its fellow of the opposite side. Sometimes it articulates with the orbital surface, 
and sometimes with the lateral pterygoid plate of the sphenoid. 

CHANGES PRODUCED IN THE MAXILLA BY AGE. 

At birth the transverse and antero-posterior diameters of the bone are each greater than the 
vertical. The frontal process is well-marked and the body of the bone consists of little more than 
the alveolar process, the teeth sockets reaching almost to the floor of the orbit. The maxillary 
sinus presents the appearance of a furrow on the lateral wall of the nose. In the adult the vertical 
diameter is the greatest, owing to the development of the alveolar process and the increase in 
size of the sinus. In old age the bone reverts in some measure to the infantile condition; its 
height is diminished, and after the loss of the teeth the alveolar process is absorbed, and the 
lower part of the bone contracted and reduced in thickness. 



The Lacrimal Bone (Os Lacrimale). 

The lacrimal bone, the smallest and most fragile bone of the face, is situated 
at the front part of the medial wall of the orbit (Fig. 164). It has two surfaces 
and four borders. 

' American Journal of Anatomj', 1906, vol. v. 

2 Journal of Anatomv and Physiology, 1911, vol. xlv. 

3 Some anatomists believe that the premaxillary bone is ossified by two centers (see page 299). 




164 OSTEOLOGY 

Surfaces. — The lateral or orbital surface (Fig. 163) is divided by a vertical ridge, 
the posterior lacrimal crest, into two parts. In front of this crest is a longitudinal 
groove, the lacrimal sulcus {sulcus lacrimalis) , the inner margin of which unites 
with the frontal process of the maxilla, and the lacrimal fossa is thus completed. 
The upper part of this fossa lodges the lacrimal sac, the lower part, the naso- 
lacrimal duct. The portion behind the crest is smooth,, and forms part of the 
medial wall of the orbit. The crest, with a part of the orbital surface imme- 
diately behind it, gives origin to the lacrimal part of the Orbicularis oculi and 
ends below in a small, hook-like projection, the lacrimal hamulus, which articu- 
lates with the lacrimal tubercle of the maxilla, and completes 
wiOFronfai the Upper orifice of the lacrimal canal; it sometimes exists as 

/j/'^k^^ \ a ^ separate piece, and is then called the lesser lacrimal bone. 

The medial or nasal surface presents a longitudinal furrow, 
corresponding to the crest on the lateral surface. The area in 
front of this furrow forms part of the middle meatus of the 
nose; that behind it articulates with the ethmoid, and completes 
some of the anterior ethmoidal cells. 

Borders. — Of the four borders the anterior articulates with 
the frontal process of the maxilla ; the posterior with the lamina 
infe^lmsai concha papyracca of the ethmoid; the superior with the frontal bone. 
Fig. 163.— Left lacri- The inferior is divided by the lower edge of the posterior lacri- 
face. ^niarged.'*^ ^""^ mal crest iuto two parts : the posterior part articulates with the 

orbital plate of the maxilla; the anterior is prolonged downward 
as the descending process, which articulates with the lacrimal process of the inferior 
nasal concha, and assists in forming the canal for the nasolacrimal duct. 

Ossification. — The lacrimal is ossified from a single center, which appears about the twelfth 
week in the membrane covering the cartilaginous nasal capsule. 

Articulations. — The lacrimal articulates with four bones: two of the cranium, the frontal 
and ethmoid, and two of the face, the maxilla and the inferior nasal concha. 

The Zygomatic Bone (Os Zygomaticum; Malar Bone). 

The zygomatic bone is small and quadrangular, and is situated at the upper 
and lateral part of the face? it forms the prominence of the cheek, part of the 
lateral wall and floor of the orbit, and parts of the temporal and infratemporal 
fossae (Fig. 164). It presents a malar and a temporal surface; four processes, the 
frontosphenoidal, orbital, maxillary, and temporal; and four borders. 

Surfaces. — The malar surface (Fig. 165) is convex and perforated near its center 
by a small aperture, the zygomaticofacial foramen, for the passage of the zygomatico- 
facial nerve and vessels; below this foramen is a slight elevation, which gives 
origin to the Zygomaticus. 

The temporal surface (Fig. 166), directed backward and medialward, is concave, 
presenting medially a rough, triangular area, for articulation with the maxilla, 
and laterally a smooth, concave surface, the upper part of which forms the anterior 
boundary of the temporal fossa, the lower a part of the infratemporal fossa. Near 
the. center of this surface is the zygomaticotemporal foramen for the transmission 
of the zygomaticotemporal nerve. 

Processes. — The frontosphenoidal process is thick and serrated, and articulates 
with the zygomatic process of the frontal bone. On its orbital surface, just within 
the orbital margin and about 11 mm. below the zygomaticofrontal suture is a 
tubercle of varying size and form, but present in 95 per cent, of skulls (WhitnalP). 

' Journal of .\natomy and Physiology, vol. xlv. The structures attached to this tubercle are: (1) the check 
ligament of the Rectus lateralis; (2) the lateral end of the aponeurosis of the Levator palpebrae superioris; (3) the 
suspensory ligament of the eye (Lockwood) ; and (4) the lateral extremities of the superior and inferior tarsi. 



THE ZYGOMATIC BONE 



165 



The orbital process is a thick, strong pLate, projecting backward and mecUahvard 
from the orbital margin. Its antero-medial surface forms, by its junction with 
the orbital surface of the maxilla and with the great wing of the sphenoid, part 
of the floor and lateral wall of the orbit. On it are seen the orifices of two canals, 



'M Parietal 




Fig. 164. — Left zygomatic bone in situ. 



the zygomaticoorbital foramina; one of these canals opens into the temporal fossa, 
the other on the malar surface of the bone; the former transmits the zygomatico- 
temporal, the latter the zygomaticofacial nerve. Its iwstero-Jateral surface, smooth 
and convex, forms parts of the temporal and infratemporal fossse. Its anterior 
margin, smooth and rounded, is part of the circumference of the orbit. Its superior 



With Frontal 



Bristles passed 

through 

zygomat ico- 

orbilal foramina 




Fig. 165. — Left zygomatic bone. Malar surface. 



Fig. 166. — Left zygomatic bone. Temporal surface. 



margin, rough, and directed horizontally, articulates with the frontal bone behind 
the zygomatic process. Its posterior margin is serrated for articulation, with the 
great wing of the sphenoid and the orbital surface of the maxilla. At the angle 
of junction of the sphenoidal and maxillary portions, a short, concave, non-articular 



166 



OSTEOLOGY 



part is generally seen; this forms the anterior boundary of the inferior orbital fissure: 
occasionally, this non-articular part is absent, the fissure then being completed 
by the junction of the maxilla and sphenoid, or by the interposition of a small 
sutural bone in the angular interval between them. The maxillary process presents 
a rough, triangular surface which articulates with the maxilla. The temporal 
process, long, narrow, and serrated, articulates with the zygomatic process of the 
temporal. 

Borders. — The antero-superior or orbital border is smooth, concave, and forms 
a considerable part of the circumference of the orbit. The antero-inferior or maxil- 
lary border is rough, and bevelled at the expense of its inner table, to articulate 
with the maxilla; near the orbital margin it gives origin to the Quadratus labii 
superioris. The postero-superior or temporal border, curved like an italic letter /, 
is continuous above with the commencement of the temporal line, and below with 
the upper border of the zygomatic arch; the temporal fascia is attached to it. 
The postero-inferior t)r zygomatic border affords attachment by its rough edge to 
the Masseter. 

Ossification. — The zygomatic bone is generally described as ossifying from three centers — 
one for the malar and two for the orbital portion; these appear about the eighth week and fuse 
about the fifth month of fetal life. Mall describes it as being ossified from one center which 
appears just beneath and to the lateral side of the orbit. After birth, the bone is sometimes 
divided by a horizontal suture into an upper larger, and a lower smaller division. In some quad- 
rumana the zygomatic bone consists of two parts, an orbital and a malar. 

Articulations. — The zygomatic articulates with /oar bones: the frontal, sphenoidal, temporal, 
and maxilla. 



Groove for 
nasolacrimal duct 



Frontal process 



Maxillary siuus 
Orbital process 



Sphenopalatine 
notch 

Sphenoidal 
process 



Conchal crest 




-Concfial crest 



Fig. 167. — Articulation of left palatine bone with maxilla. 



The Palatine Bone (Os Palatinum; Palate Bone). 

The palatine bone is situated at the back part of the nasal cavity between the 
maxilla and the pterygoid process of the sphenoid (Fig. 167). It contributes 
to the walls of three cavities: the floor and lateral wall of the nasal cavity, the 
roof of the mouth, and the floor of the orbit; it enters into the formation of two 
fossae, the pterygopalatine and pterygoid fossae; and one fissure, the inferior orbital 
fissure. The palatine bone somewhat resembles the letter L, and consists of a 
horizontal and a vertical part and three outstanding processes — viz., the pyramidal 



THE PALATINE BONE 



167 



process, which is directed backward and lateralward from the junction of the two 
parts, and the orbital and sphenoidal processes, which surmount the vertical 
part, and are separated by a deep notch, the sphenopalatine notch. 

The Horizontal Part (pars horizontalis ; horizontal plate) (Figs. 108, 169).— The 
horizontal part is quadrilateral, and has two surfaces and four borders. 

Surfaces. — The superior surface, concave from side to side, forms the back part 
of the floor of the nasal cavity. The inferior surface, slightly concave and rough, 
forms, with the corresponding surface of the opposite bone, the posterior fourth 
of the hard palate. Near its posterior margin may be seen a more or less marked 
transverse ridge for the attachment of part of the aponeurosis of the Tensor veli 
palatini. 



■^jlid Pi'oc 



Maxillary surface 



Superior meatus. 
Sphenopalatine foramen — 




/»>, 



01 



,.V'- 



SiirJ 



Maxillary 
process 



t Pterygo- 
►J palatine , 
o canal 



Sphenopalatine 
foramen 

Sphenoidal process 
Articular portion 

Non-articular 
portion 



Fig. 168.- 



HORIZONTAL PART 

-Left palatine bone. 
Enlarged. 



iifSm 


nlkiL,. ^^^3 


S Posterior 


jmiim 


l>lpp** ^ 


nasal 


/wc'^i^^^^.^BI jfl 


XjMusculus uvulae 


spine 


Pyramidal \P 


^ HORIZONTAL 




process 


PART 





Nasal aspect. 



Fig. 169. — Left palatine bone. Posterior aspect. 
Enlarged. 



Borders. — The anterior border is serrated, and articulates with the palatine process 
of the maxilla. The posterior border is concave, free, and serves for the attachment 
of the soft palate. Its medial end is sharp and pointed, and, when united with 
that of the opposite bone, forms a projecting process, the posterior nasal spine 
for the attachment of the IMusculus uvulae. The lateral border is united with 
the lower margin of the perpendicular part, and is grooved by the lower end of 
the pterygopalatine canal. The medial border, the thickest, is serrated for articu- 
lation with its fellow of the opposite side; its superior edge is raised into a ridge, 
which, united with the ridge of the opposite bone, forms the nasal crest for articu- 
lation with the posterior part of the lower edge of the vomer. 

The Vertical Part {pars perpendicularis; perpendicular plate) (Figs. 168, 169). — 
The vertical part is thin, of an oblong form, and presents two surfaces and four 
borders. 

Surfaces. — The nasal surface exhibits at its lower part a broad, shallow depres- 
sion, which forms part of the inferior meatus of the nose. Immediately above this 
is a well-marked horizontal ridge, the conchal crest, for articulation with the 
inferior nasal concha; still higher is a second broad, shallow depression, which 
forms part of the middle meatus, and is limited above by a horizontal crest less 
prominent than the inferior, the ethmoidal crest, for articulation with the middle 
nasal concha. Above the ethmoidal crest is a narrow, horizontal groove, which 
forms part of the superior meatus. 



168 OSTEOLOGY 

The maxillary surface is rough and irregular throughout the greater part of its 
extent, for articuhition with the nasal surface of the maxilla; its upper and back 
part is smooth where it enters into the formation of the pterygopalatine fossa; 
it is also smooth in front, where it forms the posterior part of the medial wall 
of the maxillary sinus. On the posterior part of this surface is a deep vertical 
groove, converted into the pterygopalatine canal, by articulation with the maxilla; 
this canal transmits the descending palatine vessels, and the anterior palatine 
nerve. 

Borders. — The anterior border is thin and irregular; opposite the conchal crest is a 
pointed, projecting lamina, the maxillary process, which is directed forward, and 
closes in the lower and back part of the opening of the maxillary sinus. The 
posterior border (Fig. 1G9) presents a deep groove, the edges of which are serrated 
for articulation with the medial pterygoid plate of the sphenoid. This border 
is continuous above with the sphenoidal process; below it expands into the 
pyramidal process. The superior border supports the orbital process in front and the 
sphenoidal process behind. These processes are separated by the sphenopalatine 
notch, which is converted into the sphenopalatine foramen by the under surface of 
the body of the sphenoid. In the articulated skull this foramen leads from the 
pterygopalatine fossa into the posterior part of the superior meatus of the nose, 
and transmits the sphenopalatine vessels and the superior nasal and nasopalatine 
nerves. The inferior border is fused with the lateral edge of the horizontal part, 
and immediately in front of the pyramidal process is grooved by the lower end 
of the pterygopalatine canal. 

The JPyramidal Process or Tuberosity (processus pyramidalis). — The pyramidal 
process projects backward and lateralward from the junction of the horizontal 
and vertical parts, and is received into the angular interval between the lower 
extremities of the pterygoid plates. On its posterior surface is a smooth, grooved, 
triangular area, limited on either side by a rough articular furrow. The furrows 
articulate with the pterygoid plates, while the grooved intermediate area completes 
the lower part of the pterygoid fossa and gives origin to a few fibers of the Ptery- 
goideus internus. The anterior part of the lateral surface is rough, for articulation 
with the tuberosity of the maxilla; its posterior part consists of a smooth triangular 
area which appears, in the articulated skull, between the tuberosity of the maxilla 
and the lower part of the lateral pterygoid plate, and completes the lower part 
of the infratemporal fossa. On the base of the pyramidal process, close to its 
union with the horizontal part, are the lesser palatine foramina for the transmis- 
sion of the posterior and middle palatine nerves. 

The Orbital Process (processus orbitalis). — The orbital process is placed on a 
higher level than the sphenoidal, and is directed upward and lateralward from 
the front of the vertical part, to which it is connected by a constricted neck. It 
presents five surfaces, which enclose an air cell. Of these surfaces, three are articu- 
lar and two non-articular. The articular surfaces are: (1) the anterior or maxillary, 
•directed forward, lateralward, and downward, of an oblong form, and rough for 
articulation with the maxilla; (2) the posterior or sphenoidal, directed backward, 
upward, and medialward; it presents the opening of the air cell, which usually 
communicates with the sphenoidal sinus; the margins of the opening are serrated 
for articulation with the sphenoidal concha; (3) the medial or ethmoidal, directed 
forward, articulates with the labvrinth of the ethmoid. In some cases the air 
cell opens on this surface of the bone and then communicates with the posterior 
ethmoidal cells. j\Iore rarely it opens on both surfaces, and then communicates 
with the posterior ethmoidal cells and the sphenoidal sinus. The non-articular 
surfaces are: (1) the superior or orbital, directed upward and lateralward; it is 
triangular in shape, and forms the back part of the floor of the orbit; and (2) the 
lateral, of an oblong form, directed toward the pterygopalatine fossa; it is separated 



THE INFERIOR NASAL CONCHA 169 

from the orbital surface by a rounded border, which enters into the formation of 
the inferior orbital fissure. 

The Sphenoidal Process (proces.ms spheuoidalis).— The sphenoidal process is 
a thin, compressed plate, much smaller than the orbital, and directed upward 
and medialward. It presents three surfaces and two borders. The superior surface 
articulates with the root of the pterygoid process and the under surface of the 
sphenoidal concha, its medial border reaching as far as the ala of the vomer; it 
presents a groove which contributes to the formation of the pharyngeal canal. 
The medial surface is concave, and forms part of the lateral wall of the nasal cavity. 
The lateral surface is divided into an articular and a non-articular portion: the 
former is rough, for articulation with the medial pterygoid plate; the latter is 
smooth, and forms part of the pterygopalatine fossa. The anterior border forms 
the posterior boundary of the sphenopalatine notch. The posterior border, ser- 
rated at the expense of the outer table, articulates with the medial pterygoid 
plate. 

The orbital and sphenoidal processes are separated from one another by the 
sphenopalatine notch. Sometimes the two processes are united above, and form 
between them a complete foramen (Fig. 1()8), or the notch may be crossed by one 
or more spicules of bone, giving rise to two or more foramina. 

Ossification. — The palatine bone is ossified in membrane from a single center, which makes 
its appearance about the sixth or eighth week of fetal life at the angle of junction of the two parts 
of the bone. From this point ossification spreads medialward to the horizontal part, downward 
into the pyramidal process, and upward into the vertical part. Some authorities describe the 
bone as ossifying from four centers: one for the pyramidal process and portion of the vertical 
part behind the pterygopalatine groove; a second for the rest of the vertical and the horizontal 
parts; a third for the orbital, and a fourth for the sphenoidal process. At the time of birth the 
height of the vertical part is about equal to the transverse width of the horizontal part, whereas 
in the adult the former measures about twice as much as the latter. 

Articulations. — The palatine articulates with six bones: the sphenoid, ethmoid, maxilla, 
inferior nasal concha, vomer, and opposite palatine. 

The Inferior Nasal Concha (Concha Nasalis Inferior; Inferior Turbinated Bone). 

The inferior nasal concha extends horizontally along the lateral wall of the 
nasal cavity (Fig. 170) and consists of a lamina of spongy bone, curled upon itself 
like a scroll. It has two surfaces, two borders, and two extremities. 

The medial surface (Fig. 171) is convex, perforated by numerous apertures, 
and traversed by longitudinal grooves for the lodgement of vessels. The lateral 
surface is concave (Fig. 172), and forms part of the inferior meatus. Its upper 
border is thin, irregular, and connected to various bones along the lateral wall 
of the nasal cavity. It may be divided into three portions: of these, the anterior 
articulates with the conchal crest of the maxilla; the posterior with the conchal 
crest of the palatine; the middle portion presents three well-marked processes, 
which vary much in their size and form. Of these, the anterior or lacrimal process 
is small and pointed and is situated at the junction of the anterior fourth with 
the posterior three-fourths of the bone: it articulates, by its apex, with the descend- 
ing process of the lacrimal bone, and, by its margins, with the groove on the back 
of the frontal process of the maxilla, and thus assists in forming the canal for the 
nasolacrimal duct. Behind this process a broad, thin plate, the ethmoidal process, 
ascends to join the uncinate process of the ethmoid; from its lower border a thin 
lamina, the maxillary process, curves downward and lateralward; it articulates 
with the maxilla and forms a part of the medial wall of the maxillary sinus. The 
inferior border is free, thick, and cellular in structure, more especially in the middle 
of the bone. Both extremities are more or less pointed, the posterior being the 
more tapering. 



170 



OSTEOLOGY 



Ossification. — The inferior nasal concha is ossified from a single center, which appears about 
the fifth month of fetal hfe in the lateral wall of the cartilaginous nasal capsule. 

Articulations. — The inferior nasal concha articulates with four bones: the ethmoid, maxilla, 
lacrimal, and palatine. 



Uncinate 
process 
oj ethmoid 



Frontal sinus 



Crista galli 



Sella turcica 




Openings into 
maxilla ry sinus 
Medial pterygoid plate 
Pterygoid hamulus 



Fig. 170. — Lateral wall of right nasal cavity showing inferior concha in situ. 




FiQ. 171. — Right inferior nasal concha. 
Medial surface. 




Fig. 172.- 



-Right inferior nasal concha. 
Lateral surface. 



The Vomer. 

The vomer is situated in the median plane, but its anterior portion is frequently 
bent to one or other side. It is thin, somewhat quadrilateral in shape, and forms 
the hinder and lower part of the nasal septum (Fig. 173) ; it has two surfaces and 
four borders. The surfaces (Fig. 174) are marked by small furrow^s for blood- 
vessels, and on each is the nasopalatine groove, which runs obliquely downward 
and forward, and lodges the nasopalatine nerve and vessels. The superior border, 
the thickest, presents a deep furrow, bounded on either side by a horizontal pro- 
jecting ala of bone; the furrow receives the rostrum of the sphenoid, while the 
margins of the alse articulate with the vaginal processes of the medial pterygoid 
plates of the sphenoid behind, and with the sphenoidal processes of the palatine 
bones in front. The inferior border articulates with the crest formed bv the maxillae 



THE VOMER 



171 



and palatine bones. The anterior border is the longest and slopes downward and 
forward. Its upper half is fused with the perpendicular plate of the ethmoid; 
its lower half is grooved for the inferior margin of the septal cartilage of the nose. 
The posterior border is free, concave, and separates the choanse. It is thick and 
bifid above, thin below. 



Crest of nasal hones 
Frontal spine 



Space for triangular 
cartilage of septum 




Crest of palatines 
Crest of maxillae 



Fig. 173. — Median wall of left nasal cavity showing vomer in situ. 

Ossification. — At an early period the septum of the nose consists of a plate of cartilage, the 
ethmovomerine cartilage. The postero-superior part of this cartilage is ossified to form the per- 
pendicular plate of the ethmoid; its antero-inferior portion persists as the septal cartilage, while 
the vomer is ossified in the membrane covering its postero-inferior part. Two ossific centers, 
one on either side of the middle line, appear about the eighth week of fetal life in this part of 
the membrane, and hence the vomer consists primarily of two lamellae. About the third month 




Fig. 174. — The vomer. 




Fig 175. — Vomer of infant. 



these unite below, and thus a deep groove is formed in which the cartilage is lodged. As 
growth proceeds, the union of the lamellae extends upward and forward, and at the same time the 
intervening plate of cartilage undergoes absorption. By the age of puberty the lamellaj are almost 
completely united to form a median plate, but evidence of the bilaminar origin of the bone is 
seen in the everted alae of its upper border and the groove on its anterior margin. 



172 



OSTEOLOGY 



Articulations.— The vomer articulates with six bones: two of the cranium, the sphenoid and 
ethmoid; and four of the face, the two maxilte and the two palatine bones; it also articulates 
with the septal cartilage of the nose. 

The Mandible (Mandibula; Inferior Maxillary Bone; Lower Jaw). 

The mandible, the largest and strongest bone of the face, serves for the reception 
of the lower teeth. It consists of a curved, horizontal portion, the body, and two 
perpendicular portions, the rami, which unite with the ends of the body nearly 
at right angles. 

The Body {corpus mandihulw). — ^The body is curved somewhat like a horseshoe, 
and has two surfaces and two borders. 

Surfaces. — The external surface (Fig. 176) is marked in the median line by a 
faint ridge, indicating the symphysis or line of junction of the two pieces of which 
the bone is composed at an early period of life. This ridge divides below and 
encloses a triangular eminence, the mental protuberance, the base of which is de- 



Coronoid process 



Condyle 



TEMrORALIS 



Mental 
protuberance 




Groove for external 
maxillary artery 

Fig. 176. — Mandible. Outer surface. Side view. 



pressed in the center but raised on either side to form the mental tubercle. On either 
side of the symphysis, just below the incisor teeth, is a depression, the incisive 
fossa, which gives origin to the jNIentalis and a small portion of the Orbicularis 
oris. Below the second premolar tooth, on either side, midway between the upper 
and lower borders of the body, is the mental foramen, for the passage of the mental 
vessels and nerve. Running backward and upward from each mental tubercle 
is a faint ridge, the oblique line, which is continuous with the anterior border of the 
ramus; it affords attachment to the Quadratus labii inferioris and Triangularis; 
the Platysma is attached below it. 

The internal surface (Fig. 177) is concave from side to side. Xear the lower 
part of the symphysis is a pair of laterally placed spines, termed the mental spines, 
which give origin to the Genioglossi. Immediately below these is a second pair 
of spines, or more frequently a median ridge or impression, for the origin of the 
Geniohyoidei. In some cases the mental spines are fused to form a single eminence, 
in others they are absent and their position is indicated merely by an irregularity 
of the surface. Above the mental spines a median foramen and furrow are some- 
times seen; they mark the line of union of the halves of the bone. Below the mental 



THE MANDIBLE 



173 



spines, on either side of the middle line, is an oval depression for the attachment 
of the anterior belly of the Digastricus. Extending upward and backward on either 
side from the lo\yer part of the symphysis is the mylohyoid line, which gives origin 
to the Mylohyoideus; the posterior part of this line, near the alveolar margin, 
gives attachment to a small part of the Constrictor pharyngis superior, and to 
the pterygomandilnilar raphe. Above the anterior part of this line is a smooth 
triangular area against which the sublingual gland rests, and below the hinder 
part, an oval fossa for the submaxillary gland. 

Borders.— The superior or alveolar border, wider behind than in front, is hollowed 
into cavities, for the reception of the teeth; these cavities are sixteen in number, 
and vary in depth and size according to the teeth which they contain. To the 
outer lip of the superior border, on either side, the Buccinator is attached as 
far forward as the first molar tooth. The inferior border is rounded, longer than 
the superior, and thicker in front than behind; at the point where it joins the 
lower border of the ramus a shallow groove; for the external maxillary artery, 
may be present. 



^iyj^.^ 




hyoideus 



Mylohyoid line 

BODY 
Fig. 177. — Mandible. Inner surface. Side view. 



Genio- 
glossics 



The Ramus {ramus mandibulcp; perpendicular portion). — The ramus is quadri- 
lateral in shape, and has two surfaces, four borders, and two processes. 

Surfaces. — The lateral surface (Fig. ITO) is flat and marked by oblique ridges 
at its lower part; it gives attachment throughout nearly the whole of its extent 
to the Masseter. The medial surface (Fig. 177) presents about its center the oblique 
mandibular foramen, for the entrance of the inferior alveolar vessels and nerve. 
The margin of this opening is irregular; it presents in front a prominent ridge, 
surmounted by a sharp spine, the lingula mandibulse, which gives attachment to 
the sphenomandibular ligament; at its lower and back part is a notch from which 
the mylohyoid groove runs obliquely downward and forward, and lodges the mylo- 
hyoid vessels and nerve. Behind this groove is a rough surface, for the insertion 
of the Pterygoideus internus. The mandibular canal runs obliquely downward 
and forward in the ramus, and then horizontally forward in the body, where it 
is placed under the alveoli and communicates with them by small openings. On 
arriving at the incisor teeth, it turns back to communicate with the mental foramen, 
giving off two small canals which run to the cavities containing the incisor teeth. 



174 OSTEOLOGY 

[n the posterior two-thirds of the bone the canal is situated nearer the internal 
surface of the mandible; and in the anterior third, nearer its external surface. It 
contains the inferior alveolar vessels and nerve, from which branches are dis- 
tributed to the teeth. The lower border of the ramus is thick, straight, and con- 
tinuous with the inferior border of the body of the bone. At its junction with the 
posterior bonier is the angle of the mandible, which may be either inverted or everted 
and is marked by rough, oblique ridges on each side, for the attachment of the 
Masseter laterally, and the Pterygoideus internus medially; the stylomandibular 
ligament is attached to the angle between these muscles. The anterior border is 
thin above, thicker below, and continuous with the oblique line. The posterior 
border is thick, smooth, rounded, and covered by the parotid gland. The upper 
border is thin, and is surmounted by two processes, the coronoid in front and the 
condyloid behind, separated by a deep concavity, the mandibular notch. 

The Coronoid Process {processus coronoideus) is a thin, triangular eminence, 
which is flattened from side to side and varies in shape and size. Its anterior 
border is convex and is continuous below with the anterior border of the ramus; 
its posterior border is concave and forms the anterior boundary of the mandibular 
notch. Its lateral surface is smooth, and affords insertion to the Temporalis and 
^Slasseter. Its medial surface gives insertion to the Temporalis, and presents 
a ridge which begins near the apex of the process and runs downward and forward 
to the inner side of the last molar tooth. Between this ridge and the anterior 
border is a grooved triangular area, the upper part of which gives attachment 
to the Temporalis, the lower part to some fibers of the Buccinator. 

The Condyloid Process (processus condyloideus) is thicker than the coronoid, 
and consists of two portions: the condyle, and the constricted portion which sup- 
ports it, the neck. The condyle presents an articular surface for articulation with 
the articular disk of the temporomandibular joint; it is convex from before back- 
ward and from side to side, and extends farther on the posterior than on the ante- 
rior surface. Its long axis is directed medialward and slightly back^vard, and if 
prolonged to the middle line will meet that of the opposite condyle near the ante- 
rior margin of the foramen magnum. At the lateral extremity of the condyle 
is a small tubercle for the attachment of the temporomandibular ligament. The 
neck is flattened from before backward, and strengthened by ridges which descend 
from the forepart and sides of the condyle. Its posterior surface is convex; its 
anterior presents a depression for the attachment of the Pterygoideus externus. 

The mandibular notch, separating the two processes, is a deep semilunar depres- 
sion, and is crossed by the masseteric vessels and nerve. 

Ossification. — The mandible is ossified in the fibrous membrane covering the outer sm-faces 
of ^Meckel's cartilages. These cartilages form the cartilaginous bar of the mandibular arch (see 
p. 66), and are two in number, a right and a left. Their proximal or cranial ends are connected 
with the ear capsules, and their distal extremities are joined to one another at the symphysis 
by mesodermal tissue. They run forward immediately below the condyles and then, bending 
downward, lie in a groove near the lower border of the bone; in front of the canine tooth they 
' incline upward to the symphysis. From the proximal end of each cartilage the malleus and 
incus, two of the bones of the middle ear, are developed; the next succeeding portion, as far as 
the lingula, is replaced by fibrous tissue, which persists to form the sphenomandibular hgament. 
Between the Mngula and the canine tooth the cartilage disappears, while the portion of it below 
and behind the incisor teeth becomes ossified and incorporated with this part of the mandible. 

Ossification takes place in the membrane covering the outer surface of the ventral end of 
Meckel's cartilage (Figs. 178 to 181), and each half of the bone is formed from a single center 
which appears, near the mental foramen, about the sLxth week of fetal hfe. By the tenth week 
the portion of Meckel's cartilage which lies below and behind the incisor teeth is surrounded and 
invaded by the membrane bone. Somewhat later, accessory nuclei of cartilage make their appear- 
ance, viz., a wedge-shaped nucleus in the condyloid process and extending downwai'd through 
the ramus; a small strip along the anterior border of the coronoid process; and smaller nuclei 
in the front part of both alveolar walls and along the front of the lower border of the bone. These 
accessory nuclei possess no separate ossific centers, but are invaded by the surrounding membrane 



THE MANDIBLE 



175 



bone and undergo absorption The inner alveolar border, usually described as arising from a 
separate ossific center [svlemal center), is formed in the human mandible by an ingrowth from 
the main mass of the bone. At birth the bone consists of two parts, united by a fibrous symphysis, 
in which ossmcation takes place during the first year. 

The foregoing description of the ossification of the mandible is based on the researches of 
Lowi and t awcett,^ and differs somewhat from that usually given. 

Articulations.— The mandible articulates with the two temporal bones. 



Mental nerve 




Lingual nerve 
Inf. alveolar n. 



Mylohyoid nerve 

Fig. 178. — Mandible of human embryo 24 mm. 
long. Outer aspect. (From model by Low.) 

Mandibular nerve 
Meckel's cartilage 

111* 




Stapes 
Facial nerve 



Mylohyoid nerve 
Chorda tympani 



RcicherVs cartilage 



FiQ. 179. — Mandible of human embryo 24 mm. long. 
Inner aspect. (From modnl by Low.) 



Mental nerve 




Anterior process of malleus 



Fig. 180. — Mandible of human embryo 95 mm. long. Outer aspect. Nuclei of cartilage stippled. 
, (From model by Low.) 



Auriculotemporal nerve 



Lingual nerve 



Meckel's 
cartilage 




Ant. process of malleus 
Chorda tympani 

Symphysis Mylohyoid nerve 

Fig. 181. — Mandible of human embryo 95 mm. long. Inner aspect. Nuclei of cartilage stippled. 

(From model by Low.) 



CHANGES PRODUCED IX THE MANDIBLE BY AGE. 



At birth (Fig. 182) the body of the bone is a mere shell, containing the sockets of the two 
incisor, the canine, and the two deciduous molar teeth, imperfectly partitioned off from one 
another. The mandibular canal is of large size, and runs near the lower border of the bone; the 
mental foramen opens beneath the socket of the first deciduous molar tooth. The angle is obtuse 
(175°), and the condyloid portion is nearly in fine with the body. The coronoid process is of 
comparatively large size, and projects above the level of the condyle. 

' Proceedings of the Anatomical and .\nthropological Society of the University of Aberdeen, 1905, and Journal of 
Anatomy and Physiology, vol. xliv. 
' Journal of the -American Medical Association, September 2, 1905. 



17G 



OSTEOLOGY 




Fi3. 182. — At birth. 




Fig. 183. — In childhood. 




Fig. 184.— In the adult. 




Fig. 185.— In old age. 
Side view of the mandible at different periods of life. 



THE HYOID BONE 



177 



After birth (Fig. 183) the two segments of the bone become joined at the symphysis, from 
below upward, m the first year; but a trace of separation may be visible in the beginning of the 
second year, near the a veolar margin. The body becomes elongated in its whole length, but 
more especially behind the mental foramen, to provide space for the three additional teeth devel- 
oped in this part. The depth of the body increases owing to increased growth of the alveolar 
part to afford room for the roots of the teeth, and by thickening of the subdental portion which 
enables the jaw to withstand the powerful action of the masticatory muscles; but the alveolar 
portion IS the deeper of the two, and, consequently, the chief part of the body lies above the 
obhque line The mandibular canal, after the second dentition, is situated just above the level 
of the mylohyoid line; and the mental foramen occupies the position usual to it in the adult 
The angle becomes less obtuse, owing to the separation of the jaws by the teeth; about the fourth 
year it is 140 . 

In the adult (Fig. 184) the alveolar and subdental portions of the body are usually of equal 
depth. The mental foramen opens midway between the upper and lower borders of the bone 
and the mandibular canal runs nearly paraUel with the mylohyoid line. The ramus is ahnost 
vertical in direction, the angle measuring from 110° to 120°. 

In old age (Fig. 1S5) the bone becomes greatly reduced in size, for with the loss of the teeth 
the alveolar process is absorbed, and, consequently, the chief part of the bone is below the obhque 
line. The mandibular canal, with the mental foramen opening from it, is close to the alveolar 
border. The ramus is oblique in direction, the angle measures about 140°, and the neck of the 
condyle is more or less bent backward. 



► 



Constrictor Pharysgis Medius^ 

HvOGLOSSUSn 

Lesser cornu Chondroglossus , 

V Genioglossus * #\ / 

)J\'/ 



The Hyoid Bone (Os Hyoideum; Lingual Bone). 

The hyoid bone is shaped like a horseshoe, and is suspended from the tips of the 
styloid processes of the temporal bones by the stylohyoid ligaments. It consists 
of five segments, viz., a body, two greater cornua, and two lesser cornua. 

The Body or Basihyal {corpus oss. h y aide i).— The body or central part is 
of a quadrilateral form. Its anterior surface (Fig. 186) is'convex and directed 
forward and upward. It is crossed in its upper half by a well-marked transverse 
ridge with a slight downward 
convexit>', and in many cases ^n^, ^Greater comu 

a vertical median ridge divides 
it into two lateral halves. 
The portion of the vertical 
ridge above the transverse line 
is present in a majority of 
specimens, but the lower por- 
tion is evident only in rare 
cases. The anterior surface 
gives insertion to the Genio- 
hyoideus in the greater part 
of its extent both above and 
below the transverse ridge; a 
portion of the origin of the 
Hyoglossus notches the lateral 
margin of the Geniohyoideus attachment. Below the transverse ridge the IMylo- 
hyoideus, Sternohyoideus, and Omohyoideus are inserted. The posterior surface is 
smooth, concave, directed backward and downward, and separated from the epi- 
glottis by the hyothyroid membrane and a quantity of loose areolar tissue; a bursa 
intervenes between it and the hyothyroid membrane. The superior border is 
roimded, and gives attachment to the hyothyroid membrane and some aponeurotic 
fibers of the Genioglossus. The inferior border affords insertion medially to the 
Sternohyoideus and laterally to the Omohyoideus and occasionally a portion of the 
Thyreohyoideus. It also gives attachment to the Levator glandulse thyreoidese, 
when this muscle is present. In early life the lateral borders are connected to 
the greater cornua by synchondroses; after middle life usually by bony union. 
12 




Body 




DIGASTRICUS <fc 
STYLOHYOIDEUS 

TllYKEOHYOIDElS 

Omohyoideus 



/ Mylohtoidecs Sternohyoideus 
Geniohyoideus 

Fig. 186. — Hyoid bone. Anterior surface. Enlarged. 



178 OSTEOLOGY 

The Greater Cornua or Thyrohyals {cornua majora). — The greater cornua 
project backward from the lateral borders of the body; they are flattened from 
above downward and diminish in size from before backward; each ends in a tubercle 
to which is fixed the lateral hyothyroid ligament. The upper surface is rough 
close to its lateral border, for muscular attachments: the largest of these are the 
origins of the Hyoglossus and Constrictor pharyngis medius which extend along 
the whole length of the cornu; the Digastricus and Stylohyoideus have small 
insertions in front of these near the junction of the body with the cornu. To the 
medial border the hyothyroid membrane is attached, while the anterior half of the 
lateral border gives insertion to the Thyreohyoideus. 

The Lesser Cornua or Ceratohyals (cornua minora). — The lesser cornu are two 
small, conical eminences, attached by their bases to the angles of junction between 
the body and greater cornua. The>' are connected to the body of the bone by fibrous 
tissue, and occasionally to the greater cornua by distinct diartlirodial joints, 
which usually persist throughout life, but occasionally become ankylosed. 

The lesser cornua are situated in the line of the transverse ridge on the body 
and appear to be morphological continuations of it (Parsons^). The apex of each 
cornu gives attachment to the stylohyoid ligament;- the Chondroglossus rises 
from the medial side of the base. 

Ossification. — The hyoid is ossified from six centers: two for the body, and one for each cornu. 
Ossification commences in the greater cornua toward the end of fetal Hfe, in the body sliortl}' 
afterward, and in the lesser cornua during the first or second year after birth. 



THE EXTERIOR OF THE SKULL. 

The skull as a whole may be viewed from different points, and the views so 
obtained are termed the normse of the skull; thus, it may be examined from above 
(norma verticalis), from below (norma basalis), from the side (norma lateralis), 
from behind (norma occipitalis), or from the front (norma frontalis). 

Norma Verticalis. — \Yhen viewed from above the outline presented varies 
greatly in different skulls; in some it is more or less oval, in others more nearly 
circular. The surface is traversed by three sutures, viz.: (1) the coronal sutures, 
nearly transverse in direction, between the frontal and parietals; (2) the sagittal 
sutm-es, medially placed, between the parietal bones, and deeply serrated in its 
anterior two-thirds; and (3) the upper part of the lambdoidal suture, between the 
parietals and the occipital. The point of junction of the sagittal and coronal suture 
is named the bregma, that of the sagittal and lambdoid sutures, the lambda; they 
indicate respectively the positions of the anterior and posterior fontanelles in the 
fetal skull. On either side of the sagittal suture are the parietal eminence and parietal 
foramen — the. latter, however, is frequently absent on one or both sides. The 
skull is often somewhat flattened in the neighborhood of the parietal foramina, 
and the term obelion is applied to that point of the sagittal suture which is on 
a level with the foramina. In front is the glabella, and on its lateral aspects are 
the superciliary arches, and above these the frontal eminences. Immediately above 
the glabella may be seen the remains of the frontal suture ; in a small percentage 
of skulls this suture persists and extends along the middle line to the bregma. 
Passing backward and upward from the zygomatic processes of the frontal bone 
are the temporal lines, which mark the upper limits of the temporal fossae. The 
zygomatic arches may or may not be seen projecting beyond the anterior portions 
of these lines. 

•See article on "The Topography and Morphology of the Human Hyoid Bone," bv F. G. Parsons, Journal of 
Anatomy and Physiology, vol. xliii. 

2 These ligaments in many animals are distinct bones, and in man may imdergo partial ossification. 



THE EXTERIOR OF THE SKULL 



179 



Norma BasaUs (Fig. 187).— The inferior surface of the base of the skull, exclu- 
sive of the mandible, is bounded in front by the incisor teeth in the maxilla?; behind, 



Incisors 



CaniTie 




Incisive canal 



Traiismils left nasopalatine nerve 
Traiijimits dencendiiuj palatine vesseh 
Transmita right nasopalatine nerve 



Lesser palatine foramina 

Posterior iiasal spine 
Musculus uvulae 
Pterygoid hamulus 



Sphenoidal process of palatine 
Pharyngeal canal 



Tensor tympani 

Pharyngeal tubercle 
Situation of auditory tuhe and 
semicanal for Tensor tympani 
Tensor veli palatini 
Inferior tympanic caiuxliculus 
Aqnaeduclus cochleae 
Jugular foramen 
Slastoid canalimlus 
Tympanomastoid fissure 



Fig. 187. — Base of skull. Inferior surface. 



180 OSTEOLOGY 

by the superior nuchal lines of the occipital; and laterally by the alveolar arch, 
the lower border of the zygomatic bone, the zygomatic arch and an imaginary 
line extending from it to the mastoid process and extremity of the superior nuchal 
line of the occipital. It is formed by the palatine processes of the maxillae and 
palatine bones, the vomer, the pterygoid processes, the under surfaces of the 
great wings, spinous processes, and part of the body of the sphenoid, the under 
surfaces of the squamae and mastoid and petrous portions of the temporals, and 
the under surface of the occipital bone. The anterior part or hard palate projects 
below the level of the rest of the surface, and is bounded in front and laterally 
by the alveolar arch containing the sixteen teeth of the maxillae. Immediately 
behind the incisor teeth is the incisive foramen. In this foramen are two lateral 
apertures, the openings of the incisive canals {foramina of Stenson) which transmit 
the anterior branches of the descending palatine vessels, and the nasopalatine 
nerves. Occasionally two additional canals are present in the incisive foramen; 
they are termed the foramina of Scarpa and are situated in the middle line; when 
present they transmit the nasopalatine nerves. The vault of the hard palate 
is concave, uneven, perforated by numerous foramina, marked by depressions for 
the palatine glands, and traversed by a crucial suture formed by the junction of the 
four bones of which it is composed. In the young skull a suture may be seen ex- 
tending on either side from the incisive foramen to the interval between the lateral 
incisor and canine teeth, and marking off the os incisivum or premaxillary bone. 
At either posterior angle of the hard palate is the greater palatine foramen, for the 
transmission of the descending palatine vessels and anterior palatine nerve; and 
running forward and medialward from it a groove, for the same vessels and nerve. 
Behind the posterior palatine foramen is the pyramidal process of the palatine bone, 
perforated by one or more lesser palatine foramina, and marked by the commence- 
ment of a transverse ridge, for the attachment of the tendinous expansion of the 
Tensor veli palatini. Projecting backward from the center of the posterior border 
of the hard palate is the posterior nasal spine, for the attachment of the jNIuscuIus 
uvulae. Behind and above the hard palate are the choanae, measuring about 
2.5 cm. in their vertical and 1.25 cm. in their transverse diameters. They are 
separated from one another by the vomer, and each is bounded above by the body 
of the sphenoid, below by the horizontal part of the palatine bone, and laterally 
by the medial pterygoid plate of the sphenoid. At the superior border of the 
vomer may be seen the expanded alae of this bone, receiving between them the ros- 
trum of the sphenoid. Near the lateral margins of the alae of the vomer, at the 
roots of the pterygoid processes, are the phar3aigeal canals. The pterygoid process 
presents near its base the pterygoid canal, for the transmission of a nerve and artery. 
The medial pterygoid plate is long and narrow ; on the lateral side of its base is the 
scaphoid fossa, for the origin of the Tensor veli palatini, and at its lower extremity 
the hamulus, around which the tendon of this muscle turns. The lateral pterygoid 
plate is broad; its lateral surface forms the medial boundary of the infratemporal 
fossa, and affords attachment to the Pterygoideus externus. 

Behind the nasal cavities is the basilar portion of the occipital bone, presenting 
near its center the pharyngeal tubercle for the attachment of the fibrous raphe 
of the pharynx, with depressions on either side for the insertions of the Rectus 
capitis anterior and Longus capitis. At the base of the lateral pterygoid plate 
is the foramen ovale, for the transmission of the mandibular nerve, the accessorv 
meningeal artery, and sometimes the lesser superficial petrosal nerve ; behind this are 
the foramen spinosum which transmits the middle meningeal vessels, and the promi- 
nent spina angularis {sphenoidal spine), which gives attachment to the spheno- 
mandibular ligament and the Tensor veli palatini. Lateral to the spina angularis 
is the mandibular fossa, divided into two parts by the petrotympanic fissure; the 
anterior portion, concave, smooth, bounded in front hv the articular tubercle, 



THE EXTERIOR OF THE SKULL 181 

serves for the articulation of the condyle of the mandible; the posterior portion, 
rough and bounded behind by the tympanic part of the temporal, is sometimes 
occupied by a part of the parotid gland. Emerging from between the laminae 
of the vaginal process of the t\mpanic part is the styloid process; and at the base 
of this process is the stylomastoid foramen, for the exit of the facial nerve, and 
entrance of the stylomastoid artery. Lateral to the stylomastoid foramen, between 
the tympanic part and the mastoid process, is the tympanomastoid fissure, for the 
auricular branch of the vagus. Upon the medial side of the mastoid process is 
the mastoid notch for the posterior belly of the Digastricus, and medial to the notch, 
the occipital groove for the occipital artery. At the base of the medial pterygoid 
plate is a large and somewhat triangular aperture, the foramen lacerum, bounded 
in front by the great wing of the sphenoid, behind by the apex of the petrous 
portion of the temporal bone, and medially by the body of the sphenoid and basilar 
portion of the occipital bone; it presents in front the posterior orifice of the ptery- 
goid canal ; behind, the aperture of the carotid canal. The lower part of this opening 
IS filled up in the fresh state by a fibrocartilaginous plate, across the upper or 
cerebral surface of which the internal carotid artery passes. Lateral to this aperture 
is a groove, the sulcus tubse auditivse, between the petrous part of the temporal and 
the great wing of the sphenoid. This sulcus is directed lateralward and backward 
from the root of the medial pterygoid plate and lodges the cartilaginous part of the 
auditory tube; it is continuous behind with the canal in the temporal bone which 
forms the bony part of the same tube. At the bottom of this sulcus is a narrow 
cleft, the petrosphenoidal fissure, which is occupied, in the fresh condition, by a 
plate of cartilage. Behind this fissure is the under surface of the petrous portion 
of the temporal bone, presenting, near its apex, the quadrilateral rough surface, 
part of Avhich affords attachment to the Levator veli palatini ; lateral to this surface 
is the orifice of the carotid canal, and medial to it, the depression leading to the 
aquseductus cochleae, the former transmitting the internal carotid artery and the 
carotid plexus of the sympathetic, the latter serving for the passage of a vein from 
the cochlea. Behind the carotid canal is the jugular foramen, a large aperture, 
formed in front by the petrous portion of the temporal, and behind by the occipital; 
it is generally larger on the right than on the left side, and may be subdivided 
into three compartments. The anterior compartment transmits the inferior 
petrosal sinus; the intermediate, the glossopharyngeal, vagus, and accessory 
nerves; the posterior, the transverse sinus and some meningeal branches from the 
occipital and ascending pharyngeal arteries. On the ridge of bone dividing the 
carotid canal from the jugular foramen is the inferior tympanic canaliculus for 
the transmission of the tympanic branch of the glossopharyngeal nerve; and on the 
wall of the jugular foramen, near the root of the styloid process, is the mastoid 
canaliculus for the passage of the auricular branch of the vagus nerve. Extending 
forward from the jugular foramen to the foramen lacerum is the petrooccipital fissure 
occupied, in the fresh state, by a plate of cartilage. Behind the basilar portion 
of the occipital bone is the foramen magnum, bounded laterally by the occipital 
condyles, the medial sides of which are rough for the attachment of the alar 
ligaments. Lateral to each condyle is the jugular process which gives attachment 
to the Rectus capitis lateralis muscle and the lateral atlantooccipital ligament. 
The foramen magnum transmits the medulla oblongata and its membranes, the 
accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, 
and the ligaments connecting the occipital bone with the axis. The mid-points 
on the anterior and posterior margins of the foramen magnum are respectively 
termed the basion and the opisthion. In front of each condyle is the canal for the 
passage of the hypoglossal nerve and a meningeal artery. Behind each condyle 
is the condyloid fossa, perforated on one or both sides by the condyloid canal, for 
the transmission of a vein from the transverse sinus. Behind the foramen magnum 



182 



OSTEOLOGY 



is the median nuchal Une ending above at the external occipital protuberance, while 
on either side are the superior and inferior nuchal lines; these, as well as the surfaces 
of bone between them, are rough for the attachment of the muscles which are 
enumerated on pages 129 and 130. 

Norma Lateralis (Fig. 188).— When viewed from the side the skull is seen to 
consist of the cranium above and behind, and of the face below and in front. The 
cranium is somewhat ovoid in shape, but its contour varies in different cases and 
depends largely on the length and height of the skull and on the degree of promi- 
nence of the superciliary arches and frontal eminences. Entering into its formation 
are the frontal, the parietal, the occipital, the temporal, and the great wing of the 




Fig. 188. — Side view of the skull. 



sphenoid. These bones are joined to one another and to the zygomatic b\' the follow- 
ing sutures: the zygomaticotemporal between the zygomatic process of the temporal 
and the temporal process of the zygomatic ; the zygomaticofrontal uniting the zygo- 
matic bone with the zygomatic process of the frontal; the sutures surrounding the 
great wing of the sphenoid, viz., the sphenozygomatic in front, the sphenofrontal 
and sphenoparietal above, and the sphenosquamosal behind. The sphcnoj^arietal 
suture varies in length in different skulls, and is absent in those cases where the 
frontal articulates with the temporal squama. The point corresponding with the 
posterior end of the sphenoparietal suture is named the pterion; it is situated about 
3 cm. behind, and a little above the level of the zygomatic process of the frontal 
bone. 



THE EXTERIOR OF THE SKULL 183 

The squamosal suture arches backward from the pterion and connects the tem- 
poral squama with the lower border of the parietal: this suture is continuous 
behind with the short, nearly horizontal parietomastoid suture, which unites the 
mastoid process of the temporal with the region of the mastoid angle of the parietal. 
Extending from above downward and forward across the cranium are the coronal 
and lambdoidal sutiires; the former connects the parietals with the frontal, the latter, 
the parietals with the occipital. The lambdoidal suture is continuous below with 
the occipitomastoid suture between the occipital and the mastoid portion of the 
temporal. In or near the last suture is the mastoid foramen, for the transmission 
of an emissary vein. The point of meeting of the parietomastoid, occipitomastoid, 
and lambdoidal sutures is known as the asterion. Immediately above the orbital 
margin is the superciliary arch, and, at a higher level, the frontal eminence. Near 
the center of the parietal bone is the parietal eminence. Posteriorly is the ex- 
ternal occipital protuberance, from which the sujjerior nuchal line may be followed 
forward to the mastoid process. Arching across the side of the cranium are the 
temporal lines, which mark the upper limit of the temporal fossa. 

The Temporal Fossa {jossa temporalis) .—The temporal fossa is bounded above 
and behind by the temporal lines, which extend from the zygomatic process of the 
frontal bone upward and backward across the frontal and parietal bones, and then 
curve downward and forward to become continuous with the supramastoid crest 
and the posterior root of the zygomatic arch. The point where the upper temporal 
line cuts the coronal suture is named the stephanion. The temporal fossa is bounded 
in front by the frontal and zygomatic bones, and opening on the back of the latter 
is the zygomaticotemporal foramen. Laterally the fossa is limited by the zygomatic 
arch, formed by the zygomatic and temporal bones; below, it is separated from the 
infratemporal fossa by the infratemporal crest on the great wing of the sphenoid, 
and by a ridge, continuous with this crest, which is carried backward across the 
temporal squama to the anterior root of the zygomatic process. In front and 
below, the fossa communicates with the orbital cavity through the inferior orbital 
or sphenomaxillary fissure. The floor of the fossa is deeply concave in front and 
convex behind, and is formed by the zygomatic, frontal, parietal, sphenoid, and 
temporal bones. It is traversed by vascular furrows; one, usually well-marked, runs 
upward above and in front of the external acoustic meatus, and lodges the middle 
temporal artery. Two others, frequently indistinct, may be observed on the 
anterior part of the floor, and are for the anterior and posterior deep temporal 
arteries. The temporal fossa contains the Temporalis muscle and its vessels and 
nerves, together with the zygomaticotemporal nerve. 

The zygomatic arch is formed by the zygomatic process of the temporal and 
the temporal process of the zygomatic, the two being united by an oblique suture; 
the tendon of the Temporalis passes medial to the arch to gain insertion into the 
coronoid process of the mandible. The zygomatic process of the temporal arises 
by two roots, an anterior, directed inward in front of the mandibular fossa, where 
it expands to form the articular tubercle, and a posterior, which runs backward 
above the external acoustic meatus and is continuous with the supramastoid 
crest. The upper border of the arch gives attachment to the temporal fascia; 
the lower border and medial surface give origin to the IMasseter. 

Below the posterior root of the zygomatic arch is the elliptical orifice of the 
external acoustic meatus, bounded in front, below, and behind by the tympanic 
part of the temporal bone; to its outer margin the cartilaginous segment of the 
external acoustic meatus is attached. The small triangular area between the 
posterior root of the zygomatic arch and the postero-superior part of the orifice is 
termed the suprameatal triangle, on the anterior border of which a small spinous 
process, the suprameatal spine, is sometimes seen. Between the tympanic part 
and the articular tubercle is the mandibular fossa, divided into two parts by the 



184 



OSTEOLOGY 



petrotympanic fissure. The anterior and larger part of the fossa articulates with 
the condyle of the mandible and is limited behind by the external acoustic meatus: 
the posterior part sometimes lodges a portion of the parotid gland. The styloid 
process extends downward and forward for a variable distance from the lower 
part of the tympanic part, and gives attachment to the Styloglossus, Stylohy- 
oideus, and Stjdopharyngeus, and to the stylohyoid and stylomandibular ligaments. 
Projecting downward behind the external acoustic meatus is the mastoid process, 
to the outer surface of which the Sternocleidomastoideus, Splenius capitis, and 
Longissimus capitis are attached. 

The Infratemporal Fossa {fossa mfratemyoralis; zygomatic fossa) (Fig. 189).— The 
infratemporal fossa is an irregularly shaped cavity, situated below and medial to the 
zygomatic arch. It is bounded, in front, by the infratemporal surface of the maxilla 



FropJra^ 



1 Parietal . 






■/eat 



i SquaT?::y 



-^ 



Inferior orbital fissure \ 
Infratemporal crest 

Pterygomaxillary fissure 



r teu^pr. ;.' ■ 




Pterygoid hamulus 

FiQ. 189. — Left infratemporal fossa. 



_>^ 



External acoustic meatus 
Tympanic part of temporal 
Styloid process 
Mandibular cavity 
Zygomatic process [cut) 

Lateral pterygoid plate 



and the ridge which descends from its zygomatic process; behind, by the articular 
tubercle of the temporal and the spina angularis of the sphenoid ; cr6oi'e, by the great 
wing of the sphenoid below the infratemporal crest, and by the under surface of 
the temporal squama; below, by the alveolar border of the maxilla; medially, by 
the lateral pterygoid plate. It contains the lower part of the Temporalis, the 
Pterygoidei internus and externus, the internal maxillary vessels, and the man- 
dibular and maxillary nerves. The foramen ovale and foramen spinosum open on 
its roof, and the alveolar canals on its anterior wall. At its upper and medial 
part are two fissures, which together form a T-shaped fissure, the horizontal limb 
being named the inferior orbital, and the vertical one the pterygomaxillary. 

The inferior orbital fissure (fissura orbitalis inferior; sphenomaxillary fissure), 
horizontal in direction, opens into the lateral and back part of the orbit. It is 
bounded above by the lower border of the orbital surface of the great wing of the 



^HE EXTERIOR OF THE SKULL 185 

sphenoid; helow, by the lateral border of the orbital surface of the maxilla and the 
orbital process of the palatine bone; laterally, by a small part of the zygomatic 
bone ■} medially, it joins at right angles with the pterygomaxillary fissure. Through 
the inferior orbital fissure the orbit communicates with the temporal, infratem- 
poral, and pterygopalatine fossae; the fissure transmits the maxillary nerve and 
its zygomatic branch, the infraorbital vessels, the ascending branches from the 
sphenopalatine ganglion, and a vein which connects the inferior ophthalmic vein 
with the pterygoid venous plexus. 

The pterygomaxillary fissure is vertical, and descends at right angles from the 
medial end of the preceding; it is a triangular interval, formed by the diver- 
gence of the maxilla from the pterygoid process of the sphenoid. It connects 
the infratemporal with the pterygopalatine fossa, and transmits the terminal part 
of the internal maxillary artery. 

The Pterygopalatine Fossa {fossa pterygopalatina; sphenomaxillary fossa). — The 
pterygopalatine fossa is a small, triangular space at the angle of junction of the 
inferior orbital and pterygomaxillary fissures, and placed beneath the apex of 
the orbit. It is bounded above by the under surface of the body of the sphenoid 
and by the orbital process of the palatine bone; in front, by the infratemporal 
surface of the maxilla; behind, by the base of the pterygoid process and lower part 
of the anterior surface of the great wing of the sphenoid; medially, by the vertical 
part of the palatine bone with its orbital and sphenoidal processes. This fossa 
communicates with the orbit by the inferior orbital fissure, with the nasal cavity 
by the sphenopalatine foramen, and with the infratemporal fossa by the pterygo- 
maxillary fissure. Five foramina open into it. Of these, three are on the posterior 
wall, viz., the foramen rotundum, the pterygoid canal, and the pharyngeal canal, 
in this order downward and medialward. On the medial wall is the sphenopalatine 
foramen, and below is the superior orifice of the pterygopalatine canal. The fossa 
contains the maxillary nerve, the sphenopalatine ganglion, and the terminal part 
of the internal maxillar}^ artery. 

Norma Occipitalis. — When viewed from behind the cranium presents a more 
or less circular outline. In the middle line is the posterior part of the sagittal 
suture connecting the parietal bones; extending downward and lateralward from 
the hinder end of the sagittal suture is the deeply serrated lambdoidal suture join- 
ing the parietals to the occipital and continuous below with the parietomastoid and 
occipitomastoid sutures; it frequently contains one or more sutural l)ones. Near 
the middle of the occipital squama is the external occipital protuberance or inion, 
and extending lateralward from it on either side is the superior nuchal line, and 
above this the faintly marked highest nuchal line. The part of the squama above 
the inion and highest lines is named the planum occipitale, and is covered by the 
Occipitalis muscle; the part below is termed the planum nuchale, and is divided 
by the median nuchal line which runs downward and forward from the inion to the 
foramen magnum; this ridge gives attachment to the ligamentum nuchse. The 
muscles attached to the planum nuchale are enumerated on p. 130. Below and in 
front are the mastoid processes, convex laterally and grooved medially by the 
mastoid notches. In or near the occipitomastoid suture is the mastoid foramen for 
the passage of the mastoid emissary vein. 

Norma Frontalis (Fig. 190). — When viewed from the front the skull exliibits a 
somewhat oval outline, limited above by the frontal bone, below by the body of the 
mandible, and laterally by the zygomatic bones and the mandibular rami. The 
upper part, formed by the frontal squama, is smooth and convex. The lower part, 
made up of the bones of the face, is irregular; it is excavated laterally by the orbital 
cavities, and presents in the middle line the anterior nasal aperture leading to the 

' Occasionally the maxilla and the sphenoid articulate with each other at the anterior extremity of this fissure: the 
zygomatic is then excluded from it. 



186 



OSTEOLOGY 



nasal cavities, and below this the transverse slit between the upper and lower 
dental arcades. Above, the frontal eminences stand out more or less prominently, 
and beneath these are the superciliary arches, joined to one another in the middle 
by the glabella. On and above the glabella a trace of the frontal suture sometimes 
persists; beneath it is the frontonasal suture, the mid-point of which is termed the 
nasion. Behind and below the frontonasal suture the frontal articulates with the 
frontal process of the maxilla and with the lacrimal. Arching transversely below 
the superciliary arches is the upper part of the margin of the orbit, thin and promi- 




Supraorbital foramen 



Superior orbital fissure 

Lamina papyracea of ethmoid 

Lacrimal 

Inferior orbital fissure 

Zygonmticofacial 'foramen 

Infraorbital foramen 
Nasal cavity 
Inferior nasal concha 



Mental foramen 



Fig. 190.— The skull from the front. 



nent in its lateral two-thirds, rounded in its medial third, and presenting, at the 
junction of these two portions, the supraorbital notch or foramen for the supra- 
orbital nerve and vessels. The supraorbital margin ends laterally in the zygomatic 
process which articulates with the zygomatic bone, and from it the temporal line 
extends upward and backward. Below the frontonasal suture is the bridge of the 
nose, convex from side to side, concavo-convex from above downward, and formed 
by the two nasal bones supported in the middle line by the perpendicular plate 
of the ethmoid, and laterally by the frontal processes of the maxillae which are 
prolonged upward between the nasal and lacrimal bones and form the lower and 



THE EXTERIOR OF THE SKULL 



187 



medial part of the circumference of each orbit. Below the nasal bones and between 
the maxilke is the anterior aperture of the nose, pyriform in shape, with the narrow 
end directed upward. Laterally this opening is bounded by sharp margins, to 
which the lateral and alar cartilages of the nose are attached; helow, the margins 
are thicker and curve medialward and forward to end in the anterior nasal spine. 
On looking into the nasal cavity, the bony septum which separates the nasal 
cavities presents, in front, a large triangular deficiency; this, in the fresh state, 
is filled up by the cartilage of the nasal septum; on the lateral wall of each nasal 
cavity the anterior part of the inferior nasal concha is visible. Below and lateral 
to the anterior nasal aperture are the anterior surfaces of the maxillee, each 
perforated, near the lower margin of the orbit, by the infraorbital foramen for the 

Nasal bone 

Lacrfmal sulcus 

Zygomatic hone 
Maxilla 



Ant. ethmoidal cells 

Nasal septum 

Probe in 
infundibulum 

Middle elhmx)idal cells 

Superior 7iasal concha 

Post, ethmoidal cells 

Superior meatus 



Sphenoidal sinuses 




Infraorbital groove 



Inferior orbital 
fissure 

Palatine bone 



Sphenoidal bone 
Foramen roiundum 



Foramen ovale 
_ Foramen spinosum 



Carotid canal 
Fig. 191. — Horizontal section of nasal and orbital cavities. 



passage of the infraorbital nerve and vessels. Below and medial to this foramen 
is the canine eminence separating the incisive from the canine fossa. Beneath 
these fossae are the alveolar processes of the maxillae containing the upper teeth, 
which overlap the teeth of the mandible in front. The zygomatic bone on either 
side forms the prominence of the cheek, the lower and lateral portion of the orbital 
cavity, and the anterior part of the zygomatic arch. It articulates medially with 
the maxilla, behind with the zygomatic process of the temporal, and above with 
the great wing of the sphenoid and the zygomatic process of the frontal; it is per- 
forated by the zygomaticofacial foramen for the passage of the zygomaticofacial 
nerve. On the body of the mandible is a median ridge, indicating the position 
of the symphysis; this ridge divides below to enclose the mental protuberance, the 
lateral angles of which constitute the mental tubercles. Below the incisor teeth 



188 



OSTEOLOGY 



is the incisive fossa, and beneath the second premolar tooth the mental foramen 
which transmits the mental nerve and vessels. The oblique line runs upward from 
the mental tubercle and is continuous behind with the anterior border of the ramus. 
The posterior border of the ramus runs downward and forward from the condyle 
to the angle, which is frequently more or less everted. 

The Orbits (orbitce) (Fig. 190). — The orbits are two quadrilateral pyramidal cavi- 
ties, situated at the upper and anterior part of the face, their bases being directed 
forward and lateralward, and their apices backward and medialward, so that their 
long axes, if continued backward, would meet over the body of the sphenoid. 
Each presents for examination a roof, a floor, a medial and a lateral wall, a base, 
and an apex. 



Anterior 
ethmoidal foramen 



Posterior ethmoidal foramen 
Orbital 'process of pilatine 
Optic foramen 

Sphenopalatine foramen 

Sella turcica 
Probe in foramen rotundum 



Fossa for 

lacrimal sac 

Uncinate process 
of ethmoid 
Openings of 
maxillary sinns 
Inferior nasal' 
concha, 




Probe in pterygoid cava 
(^^Prdbe in pterygopalatine canal 

/^^ Palatine hone 

ml 

Lateral pterygoid plate 



Pyramidal process cf palatine 



Fig. 192.— Medial wall of left orbit. 

The roof is concave, directed downward, and slightly forward, and formed in 
front by the orbital plate of the frontal; behind by the small wing of the sphenoid. 
It presents medially the trochlear fovea for the attachment of the cartilaginous 
pulley of the Obliquus oculi superior; laterally, the lacrimal fossa for the lacrimal 
gland; and posteriorly, the suture between the frontal bone and the small wing 
of the sphenoid. ' 

The floor is directed upward and lateralward, and is of less extent than the 
roof; it is formed chiefly by the orbital surface of the maxilla; m front and laterally, 
by the orbital process of the zygomatic bone, and behind and medially, to a small 
extent, by the orbital process of the palatine. At its medial angle is the upper 
opening of the nasolacrimal canal, immediately to the lateral side of which is a 
depression for the origin of the Obliquus oculi inferior. On its lateral part is the 
suture between the maxilla and zygomatic bone, and at its posterior part that 
between the maxilla and the orbital process of the palatine. Running forward 
near the middle of the floor is the infraorbital groove, ending in front in the infra- 
orbital canal and transmitting the infraorbital nerve and vessels. 



THE INTERIOR OF THE SKVLL 189 

The medial wall (Fig. 192) is nearly vertical, and is formed from before back- 
ward by the frontal process of the maxilla, the lacrimal, the lamina papyracea 
of the ethmoid, and a small part of the body of the sphenoid in front of the optic 
foramen. Sometimes the sphenoidal concha forms a small part of this wall (see 
page 152). It exhibits three vertical sutures, viz., the lacrimomaxillary, lacrimo- 
ethmoidal, and sphenoethmoidal. In front is seen the lacrimal groove, which lodges 
the lacrimal sac, and behind the groove is the posterior lacrimal crest, from which 
the lacrimal part of the Orbicularis oculi arises. At the junction of the medial 
wall and the roof are the frontomaxillary, frontolacrimal, frontoethmoidal, and 
sphenofrontal sutures. The point of junction of the anterior border of the lacrimal 
with the frontal is named the dacryon. In the frontoethmoidal suture are the 
anterior and posterior ethmoidal foramina, the former transmitting the nasociliary 
nerve and anterior ethmoidal vessels, the latter the posterior ethmoidal nerve and 
vessels. 

The lateral wall, directed medialward and forward, is formed by the orbital 
process of the zygomatic and the orbital surface of the great wing of the sphenoid; 
these are united by the sphenozygomatic suture which terminates below at the 
front end of the inferior orbital fissure. On the orbital process of the zygomatic 
bone are the orbital tubercle (Whitnall) and the orifices of one or two canals which 
transmit the branches of the zygomatic nerve. Between the roof and the lateral 
wall, near the apex of the orbit, is the superior orbital fissure. Through this fissure 
the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the 
abducent nerves enter the orbital cavity, also some filaments from the cavernous 
plexus of the sympathetic and the orbital branches of the middle meningeal artery. 
Passing backward through the fissure are the ophthalmic vein and the recurrent 
branch from the lacrimal artery to the dura mater. The lateral wall and the floor 
are separated posteriorly by the inferior orbital fissure which transmits the maxillary 
nerve and its zygomatic branch, the infraorbital vessels, and the ascending branches 
from the sphenopalatine ganglion. 

The base of the orbit, quadrilateral in shape, is formed above by the supra- 
orbital arch of the frontal bone, in which is the supraorbital notch or foramen for 
the passage of the supraorbital vessels and nerve; helow by the zygomatic bone and 
maxilla, united by the zygomaticomaxillary suture; laterally by the zygomatic 
bone and the zygomatic process of the frontal joined by the zygomaticofrontal 
suture; medially by the frontal bone and the frontal process of the maxilla united 
by the frontomaxillary suture. 

The apex, situated at the back of the orbit, corresponds to the optic foramen^ 
a short, cylindrical canal, which transmits the optic nerve and ophthalmic artery. 

It will thus be seen that there are nine openings communicating with each 
orbit, viz., the optic foramen, superior and inferior orbital fissures, supraorbital 
foramen, infraorbital canal, anterior and posterior ethmoidal foramina, zygomatic 
foramen, and the canal for the nasolacrimal duct. 

THE INTERIOR OF THE SKULL. 

Inner Surface of the Skull-cap. — The inner surface of the skull-cap is concave 
and presents depressions for the convolutions of the cerebrum, together with 
numerous furrows for the lodgement of branches of the meningeal vessels. Along 
the middle line is a longitudinal groove, narrow^ in front, where it commences at 
the frontal crest, but broader behind; it lodges the superior sagittal sinus, and its 
margins afford attachment to the falx cerebri. On either side of it are several 

' Some anatomists describe ttie apex of the orbit as corresponding with tlie medial end of the superior orbital fissure. 
It seems better, however, to adopt the statement in the text, since the ocular muscles take origin around the optic 
foramen, and diverge from it to the bulb of the eye. 



190 OSTEOLOGY 

depressions for the arachnoid granulations, and at its back part, the openings of 
the parietal foramina when these are present. It is crossed, in front, by the coronal 
suture, and behind by the lambdoidal, while the sagittal lies in the medial plane 
between the parietal bones. 

Upper Surface of the Base of the Skull (Fig. 193). — The upper surface of the 
base of the skull or floor of the cranial cavity presents three fossse, called the anterior, 
middle, and posterior cranial fossae. 

Anterior Fossa (fossa cranii anterior). — The floor of the anterior fossa is formed 
by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the 
small wings and front part of the body of the sphenoid ; it is limited behind by the 
posterior borders of the small wings of the sphenoid and by the anterior margin 
of the chiasmatic groove. It is traversed by the frontoethraoidal, sphenoethmoidal, 
and sphenofrontal sutures. Its lateral portions roof in the orbital cavities and sup- 
port the frontal lobes of the cerebrum ; they are convex and marked by depressions 
for the brain convolutions, and grooves for branches of the meningeal vessels. 
The central portion corresponds with the roof of the nasal cavity, and is markedly 
depressed on either side of the crista galli. It presents, in and near the median 
line, from before backward, the commencement of the frontal crest for the attach- 
ment of the falx cerebri; the foramen cecum, between the frontal bone and the crista 
galli of the ethmoid, which usually transmits a small vein from the nasal cavity 
to the superior sagittal sinus; behind the foramen cecum, the crista galli, the 
free margin of which affords attachment to the falx cerebri; on either side of the 
crista galli, the olfactory groove formed by the cribriform plate, which supports 
the olfactory bulb and presents foramina for the transmission of the olfactory 
nerves, and in front a slit-like opening for the nasociliary nerve. Lateral to either 
olfactory groove are the internal openings of the anterior and posterior ethmoidal 
foramina; the anterior, situated about the middle of the lateral margin of the olfac- 
tory groove, transmits the anterior ethmoidal vessels and the nasociliary nerve; the 
nerve nms in a groove along the lateral edge of the cribriform plate to the slit-like 
opening above mentioned; the posterior ethmoidal foramen opens at the back part 
of this margin under cover of the projecting lamina of the sphenoid, and transmits 
the posterior ethmoidal vessels and nerve. Farther back in the middle line is the 
ethmoidal spine, bounded behind b}' a slight elevation separating two shallow lon- 
gitudinal grooves which support the olfactory lobes. Behind this is the anterior 
margin of the chiasmatic groove, running lateralward on either side to the upper 
margin of the optic foramen. 

The Middle Fossa (fossa cranii media). — The middle fossa, deeper than the pre- 
ceding, is narrow in the middle, and wide at the sides of the skull. It is bounded 
in front by the posterior margins of the small wings of the sphenoid, the anterior 
clinoid processes, and the ridge forming the anterior margin of the chiasmatic 
groove; behind, by the superior angles of the petrous portions of the temporals 
and the dorsum sellae; laterally by the temporal squamae, sphenoidal angles of the 
parietals, and great wings of the sphenoid. It is traversed by the squamosal, 
sphenoparietal, sphenosquamosal, and sphenopetrosal sutures. 

The middle part of the fossa presents, in front, the chiasmatic groove and tuber- 
culum sellae; the chiasmatic groove ends on either side at the optic foramen, which 
transmits the optic nerve and ophthalmic artery to the orbital cavity. Behind 
the optic foramen the anterior clinoid process is directed backward and medialward 
and gives attachment to the tentorium cerebelli. Behind the tuberculum sellse 
is a deep depression, the sella turcica, containing the fossa hypophyseos, which lodges 
the hypophysis, and presents on its anterior wall the middle clinoid processes. 
The sella turcica is bounded posteriorly by a quadrilateral plate of bone, the dorsum 
sellae, the upper angles of which are surmounted by the posterior clinoid processes: 
these afford attachment to the tentorium cerebelli, and below each is a notch for 



THE INTERIOR OF THE SKULL 



191 



the abducent nerve. On either side of the sella turcica is the carotid groove, which 
is broad, shallow, and curved somewhat like the italic letter /. It begins behind 



Groove for super, sagittal sinus 

Grooves for anter. meningeal vessels 

Foramen ccecum- 

Crista galli 

Slit for nasociliary nerve 

Groove/or naxociliary nerve 

Anterior ethmoidal foramen 

Orifices for olfactory nerves 

Posterior ethmoidal foramen 

Ethmoidal spine 



Olfactory grooves 

Optic foramen 

Chiasmatic groove 

Tuberculnm sellae 

Anterior clinoid process 

Middle clinoid process 

Posterior clinoid process 

Groove for abducent nerve 

Foramen lacerum 

Orifice of carotid canal 

Depression for semilunar ganglion 



Internal acoustic meatus 

Slit for dura mater 

Groove for superior petrosal sinus 

Jugular foramen 

Hypoglossal canal 

Aqxicediictus vestihuli 

Condyloid foramen 



Mastoid foramen 
Posterior meningeal grooves 




Fig. 193. — Base of the skull. Upper surface. 



at the foramen lacerum, and ends on the medial side of the anterior clinoid process, 
where it is sometimes converted into a foramen (carotico-dmoid) by the union ot 
the anterior with the middle clinoid process; posteriorly, it is bounded laterally 



192 OSTEOLOGY 

by the lingula. This groove lodges the cavernous sinus and the internal carotid 
artery, the latter being surrounded by a plexus of sympathetic nerves. 

The lateral parts of the middle fossa are of considerable depth, and support 
the temporal lobes of the brain. They are marked by depressions for the brain 
convolutions and traversed by furrows for the anterior and posterior branches 
of the middle meningeal vessels. These furrows begin near the foramen spinosum, 
and the anterior runs forward and upward to the sphenoidal angle of the parietal, 
where it is sometimes converted into a bony canal ; the posterior runs lateralward 
and backward across the temporal squama and passes on to the parietal near 
the middle of its lower border. The following apertures are also to be seen. In 
front is the superior orbital fissure, bounded above by the small wing, below, by the 
great wing, and medially, by the body of the sphenoid; it is usually completed 
laterally by the orbital plate of the frontal bone. It transmits to the orbital 
cavity the oculomotor, the trochlear, the ophthalmic division of the trigeminal, 
and the abducent nerves, some filaments from the cavernous plexus of the 
sympathetic, and the orbital branch of the middle meningeal artery ; and from the 
orbital cavity a recurrent branch from the lacrimal artery to the dura mater, and 
the ophthalmic veins. Behind the medial end of the superior orbital fissure is 
the foramen rotundum, for the passage of the maxillary nerve. Behind and lateral 
to the foramen rotundum is the foramen ovale, which transmits the mandibular 
nerve, the accessory meningeal artery, and the lesser superficial petrosal nerve. ^ 
Medial to the foramen ovale is the foramen VesaUi, which varies in size in different 
individuals, and is often absent; when present, it opens below at the lateral side 
of the scaphoid fossa, and transmits a small vein. Lateral to the foramen ovale 
is the foramen spinosum, for the passage of the middle meningeal vessels, and a 
recurrent branch from the mandibular nerve. INIedial to the foramen ovale is 
the foramen lacenim; in the fresh state the lower part of this aperture is filled up 
by a layer of fibrocartilage, while its upper and inner parts transmit the internal 
carotid artery surrounded by a plexus of sympathetic nerves. The nerve of the 
pterygoid canal and a meningeal branch from the ascending pharyngeal artery 
pierce the layer of fibrocartilage. On the anterior surface of the petrous portion 
of the temporal bone are seen the eminence caused by the projection of the superior 
semicircular canal; in front of and a little lateral to this a depression corresponding 
to the roof of the tympanic cavity; the groove leading to the hiatus of the facial 
canal, for the transmission of the greater superficial petrosal nerve and the petrosal 
branch of the middle meningeal artery; beneath it, the smaller groove, for the pas- 
sage of the lesser superficial petrosal nerve; and, near the apex of the bone, the 
depression for the semilunar ganglion and the orifice of the carotid canal. 

The Posterior Fossa {fossa cranii posterior). — The posterior fossa is the largest 
and deepest of the three. It is formed by the dorsum sella? and clivus of the 
sphenoid, the occipital, the petrous and mastoid portions of the temporals, and the 
mastoid angles of the parietal bones; it is crossed by the occipitomastoid and the 
parietomastoid sutures, and lodges the cerebellum, pons, and medulla oblongata. 
It is separated from the middle fossa in and near the median line by the dorsum 
sellae of the sphenoid and on either side by the superior angle of the petrous por- 
tion of the temporal bone. This angle gives attachment to the tentorum cerebelli, 
is grooved for the superior petrosal sinus, and presents at its medial end a notch 
upon which the trigeminal nerve rests. The fossa is limited behind by the grooves 
for the transverse sinuses. In its center is the foramen magnum, on either side of 
which is a rough tubercle for the attachment of the alar ligaments; a little above 
this tubercle is the canal, which transmits the hypoglossal nerve and a meningeal 
branch from the ascending pharyngeal artery. In front of the foramen magnum 

' See footnote, page 150. 



THE INTERIOR OF THE SKULL 



193 



the basilar portion of the occipital and the posterior part of the body of the sphenoid 
form a grooved surface which supports the medulla oblongata and pons; in the 
young skull these bones are joined by a synchondrosis. This grooved surface is 
separated on either side from the petrous portion of the temporal by the petro- 
occipital fissure, which is occupied in the fresh state by a plate of cartilage; the 
fissure is continuous behind with the jugular foramen, and its margins are grooved 
for the inferior petrosal sinus. The jugular foramen is situated between the lateral 
part of the occipital and the petrous part of the temporal. The anterior portion 
of this foramen transmits the inferior petrosal sinus; the posterior i)ortiou, the 
transverse sinus and some meningeal branches from the occipital and ascending 
pharyngeal arteries; and the intermediate portion, the glossopharyngeal, vagus, 
and accessory nerves. Above the jugular foramen is the internal acoustic meatus, 
for the facial and acoustic nerves and internal auditory artery; behind and lateral 



Nasal bone 



Frontal process 
of maxilla 
Inf. nasal concha 



I 

I 

I 




Palatine bone 
Fig. 194. — Sagittal section of skull. 



to this is the slit-like opening leading into the aquceductus vestibuli, which lodges 
the ductus endolymphaticus; while between these, and near the superior angle of 
the petrous portion, is a small triangular depression, the remains of the fossa sub- 
arcuata, which lodges a process of the dura mater and occasionally transmits a small 
vein. Behind the foramen magnum are the inferior occipital fossae, which support 
the hemispheres of the cerebellum, separated from one another by the internal 
occipital crest, which serves for the attachment of the falx cerebelli, and lodges 
the occipital sinus. The posterior fossae are surmounted by the deep grooves for 
the transverse sinuses. Each of these channels, in its passage to the jugular foramen, 
grooves the occipital, the mastoid angle of the parietal, the mastoid portion of the 
temporal, and the jugular process of the occipital, and ends at the back part of 
the jugular foramen. Where this sinus grooves the mastoid portion of the temporal, 
the orifice of the mastoid foramen may be seen; and, just previous to its termina- 
tion, the condyloid canal opens into it ; neither opening is constant. 
. 13 



194 



OSTEOLOGY 



The Nasal Cavity {cavum nasi; nasal fossa). — The nasal cavities are two irregular 
spaces, situated one on either side of the middle line of the face, extending from the 
base of the cranium to the roof of the mouth, and separated from each other by a 
thin vertical septum. They open on the face through the pear-shaped anterior nasal 
aperture, and their posterior openings or choanae communicate, in the fresh 
state, with the nasal part of the pharynx. They are much narrower above than 
below, and in the middle than at their anterior or posterior openings: their depth, 
which is considerable, is greatest in the middle. They communicate with the 
frontal, ethmoidal, sphenoidal, and maxillary sinuses. Each cavity is bounded 
by a roof, a floor, a medial and a lateral wall. 

The roof (Figs. 195, 196) is horizontal in its central part, but slopes down- 
ward in front and behind ; it is formed in front by the nasal bone and the spine 
of the frontal ; in the middle, by the cribriform plate of the ethmoid ; and behind, 



Crest of nasal bones 
Frontal spine 



Space for triangular 
cartilage of septum 




— Crest of palatines 
Crest of maxillos 



Fig. 195. — Medial wall of left nasal fossa. 



by the body of the sphenoid, the sphenoidal concha, the ala of the vomer and the 
sphenoidal process of the palatine bone. In the cribriform plate of the ethmoid 
are the foramina for the olfactory nerves, and on the posterior part of the roof 
is the opening into the sphenoidal sinus. 

The floor is flattened from before backward and concave from side to side. 
It is formed by the palatine process of the maxilla and the horizontal part of 
the palatine bone; near its anterior end is the opening of the incisive canal. 

The medial wall {septum nasi) (Fig. 195), is frequently deflected to one or other 
side, more often to the left than to the right. It is formed, in front, by the crest 
of the nasal bones and frontal spine; in the middle, by the perpendicular plate 
of the ethmoid; behind, by the vomer and the rostrum of the sphenoid; below, 
by the crest of the maxillae and palatine bones.- It presents, in front, a large, 
triangular notch, which receives the cartilage of the septum; and behind, the 
free edge of the vomer. Its surface is marked by numerous furrows for vessels 



THE INTERIOR OF THE SKULL 



195 



and nerves and by the grooves for the nasopalatine nerve, and is traversed by 
sutures connecting the bones of which it is formed. 

The lateral wall (Fig. 196) is formed, in front, by the frontal process of the 
maxilla and by the lacrimal bone; in the middle, by the ethmoid, maxilla, and 
inferior nasal concha; behind, by the vertical plate of the palatine bone, and the 
medial pterygoid plate of the sphenoid. On this wall are three irregular antero- 
posterior passages, termed the superior, middle, and inferior meatuses of the nose. 
The superior meatus, the smallest of the three, occupies the middle third of the 
lateral wall. It lies between the superior and middle nasal conchfe; the spheno- 
palatine foramen opens into it behind, and the posterior ethmoidal cells in front. 
The sphenoidal sinus opens into a recess, the sphenoethmoidal recess, which is placed 
above and behind the superior concha. The middle meatus is situated between the 
middle and inferior conchse, and extends from the anterior to the posterior end of 



Nasal bone 
Frontal spine 

Cribriform plate of ethmoid^ 
Sphenoid 



Probe passed through 

nasolacrimal canal 
Bristle passed through 
infundibulum 



Anterior nasal spine 

Palatine proc. of naxilla 

Horizontal part of palatin 

Posterior nasal spine 

Incisive canal 




Frontal pror. of maxilla 

Larritnal 

Ethmoid 

Uncinate proc. of ethmoid 
Inferior nasal concha 
Palatine 

— -Superior meatus 
Middle meatus 
Inferior meatus 



Fig. 196. — Roof, floor, and lateral wall of left nasal cavity. 

the latter. The lateral wall of this meatus can be satisfactorily studied only after 
the removal of the middle concha. On it is a curved fissure, the hiatus semilunaris, 
limited below by the edge of the uncinate process of the ethmoid and above by 
an elevation named the bulla ethmoidalis; the middle ethmoidal cells are contained 
within this bulla and open on or near to it. Through the hiatus semilunaris 
the meatus communicates with a curved passage termed the infundibulum, which 
communicates in front with the anterior ethmoidal cells and in rather more than 
fifty per cent, of skulls is continued upward as the frontonasal duct into the frontal 
air-sinus; when this continuity fails, the frontonasal duct opens directly into the 
anterior part of the meatus. Below the bulla ethmoidalis and hidden by the unci- 
nate process of the ethmoid is the opening of the maxillary sinus (ostium maxillare) ; 
an accessory opening is frequently present above the posterior part of the inferior 
nasal concha. The inferior meatus, the largest of the three, is the space between 
the inferior concha and the floor of the nasal cavitv. It extends almost the entire 



196 



OSTEOLOGY 



length of the lateral wall of the nose, is broader in front than behind, and presents 
anteriorly the lower orifice of the nasolacrimal canal. 

The Aiiterior Nasal Aperture (Fig. 181) is a heart-shaped or pyriform opening, 
whose long axis is vertical, and narrow end upward ; in the recent state it is much 
contracted by the lateral and alar cartilages of the nose. It is bounded above by 
the inferior borders of the nasal bones; laterally by the thin, sharp margins which 
separate the anterior from the nasal surfaces of the maxillse; and helow by the same 
borders, where they curve medialward to join each other at the anterior nasal 

spine. 

The choanse are each bounded above by the under surface of the body of the 
sphenoid and ala of the vomer; helow, by the posterior border of the horizontal 
part of the palatine bone; laterally, by the medial pterygoid plate; they are 
separated from each other by the posterior border of the vomer. 



DIFFERENXES IX THE SKULL DUE TO AGE. 

At birth the skull is large in proportion to the other parts of the skeleton, but its facial portion 
is small, and equals only about one-eighth of the bulk of the cranium as compared with one-half 
in the adult. The frontal and parietal eminences are prominent, and the greatest width of the 

skull is at the level of the latter; on the other 
Frontal Jontand hand, the glabella, supercihary arches, and 

mastoid processes are not developed. Ossi- 
fication of the skull bones is not completed, 
and many of them, e. g., the occipital, temp- 
orals, sphenoid, frontal, and mandible, consist 
of more than one piece. Unossified mem- 
branous intervals, termed fontanelles, are seen 
at the angles of the parietal bones; these 
fontaneUes are six in number: two, an ante- 
rior and a posterior, are situated in the middle 
Une, and two, an antero-lateral and a postero- 
lateral, on either side. 

The anterior or bregmatic fontanelle (Fig. 
197) is the largest, and is placed at the junc- 
tion of the sagittal, coronal, and frontal 
sutures; it is lozenge-shaped, and measures 
about 4 cm. in its antero-posterior and 2.5 
cm. in its transverse diameter. The 'posterior 
fontanelle is triangular in form and is situated 
at the junction of the sagittal and lambdoidal 
sutures. The lateral fontanelles (Fig. 19S) are 
small, irregular in shape, and correspond re- 
spectively with the sphenoidal and mastoid 
angles of the parietal bones. An additional 
fontanelle is sometimes seen in the sagittal 
suture at the region of the obeUon. The 
fontanelles are usuallj'^ closed by the growth 
and extension of the bones which surroimd 
them, but sometimes they are the sites of 
separate ossific centers which develop into 
sutural bones. The posterior and lateral fon- 
tanelles are obliterated within a month or two after birth, but the anterior is not completely 
closed imtil about the middle of the second j'ear. 

The smaUness of the face at birth is mainly accounted for by the rudimentary- condition of 
the maxillse and mandible, the non-eruption of the teeth, and the small size of the maxillary air 
sinuses and nasal cavities. At birth the nasal cavities he almost entirely between the orbits, and 
the lower border of the anterior nasal aperture is only a httle below the level of the orbital floor. 
With the eruption of the deciduous teeth there is an enlargement of the face and jaws, and these 
changes are still more marked after the second dentition. 

The skull grows rapidly from birth to the seventh j'ear, by which time the foramen magnum 
and petrous parts of the temporals have reached their fuU size and the orbital cavities are only 
a little smaller than those of the adult. Growth is slow from the seventh year until the approach 




Occipital fontanel 



Fig. 197. — Skull at birth, showing frontal and occipital 

fonticuli. 



CRANIOLOGY 



197 



of puberty, when a second period of activity occurs: this results in an increase in all directions, 
but it IS especially marked in the frontal and facial regions, where it is associated with the develop- 
ment of the air sinuses. 

ObUteration of the sutures of the vault of the skull takes place as age advances. This process 
may commence between the ages of thirty and forty, and is first seen on the inner surface, and 
some ten years later on the outer surface of the skull. The dates given are, however, only approxi- 
mate, as it is impossible to state with anything hke accuracy the time at which the sutures are 
closed. Obhteration usually occurs first in the posterior part of the sagittal suture, next in the 
coronal, and then in the lambdoidal. 

In old age the skull generally becomes thinner and Ughter, but in a small proportion of cases 
it increases in thickness and weight, owing to an hypertrophy of the inner table. The most strik- 
ing feature of the old skull is the diminution in the size of the maxilla; and mandible consequent 
on the loss of the teeth and the absorption of the alveolar processes. This is associated with a 
marked reduction in the vertical measurement of the face and with an alteration in the angles 
of the mandible. 

Frontal fontanel 




Mastoid fontanel 



Sphenoidal fontanel 
Fig. 198. — Skull at birth, showing sphenoidal and mastoid fonticuli. 



SEXUAL DIFFERENCES IN THE SKULL. 

Until the age of puberty there is Httle difference between the skull of the female and that of 
the male. The skull of an adult female is, as a rule, Ughter and smaller, and its cranial capacity 
about 10 per cent, less, than that of the male. Its walls are thinner and its muscular ridges less 
strongly marked; the glabella, supercihary arches, and mastoid processes are less prominent, 
and the corresponding air sinuses are small or rudimentary. The upper margin of the orbit is 
sharp, the forehead vertical, the frontal and parietal eminences prominent, and the vault some- 
what flattened. The contour of the face is more rounded, the facial bones are smoother, and the 
maxillae and mandible and their contained teeth smaller. From what has been said it wiU be seen 
that more of the infantile characteristics are retained in the skull of the adult female than in that 
of the adult male. A well-marked male or female skuU can easily be recognized as such, but in 
some cases the respective characteristics are so indistinct that the determination of the sex may 
be difficult or impossible. 

CRANIOLOGY. 

Skulls vary in size and shape, and the term craniology is applied to the study of these varia- 
tions. The capacity of the cranial cavity constitutes a good index of the size of the bram which 
it contained, and is most conveniently arrived at by filhng the cavity with shot and measuring 
the contents in a graduated vessel. Skulls may be classified according to their capacities as 
follows : 

1. Microcephalic, with a capacity of less than 1350 c.cm. — e. g., those of native Australians 
and Andaman Islanders. 

2. Mesocephalic, with a capacity of from 1350 c.cm. to 1450 c.cm. — e. g., those of African 
negroes and Chinese. 

3 Megacephalic, with a capacity of over 1450 c.cm. — e. g., those of Europeans, Japanese, and 
Eskimos. 



198 OSTEOLOGY 

In comparing the shape of one skull with that of another it is necessary to adopt some definite 
position in which the skulls should be placed during the process of examination. They should 
be so placed that a line carried through the lower margin of the orbit and upper margin of the 
external acoustic meatus is in the horizontal plane. The normae of one skuU can then be com- 
pared with those of another, and the differences in contour and surface form noted. Further, 
it is necessary that the various hnear measurements used to determine the shape of the skull 
ehould be made between definite and easily localized points on its surface. The principal points 
may be divided into two groups: (1) those in the median plane, and (2) those on either side of it'. 

The Points in the Median Plane are the: 

Mental Point. The most prominent point of the chin. 

Alveolar Point or Prosthion. The central point of the anterior margin of the upper alveolar 
arch. 

Subnasal Point. The middle of the lower border of the anterior nasal aperture, at the base 
of the anterior nasal spine. 

Nasion. The central point of the frontonasal suture. 

Glabella. The point in the middle line at the level of the superciliary arches. 

Ophryon. The point in the middle Une of the forehead at the level where the temporal lines 
most nearly approach each other. 

Bregma. The meeting point of the coronal and sagittal sutures. 

Obelion. A point in the sagittal suture on a level with the parietal foramina. 

Lambda. The point of junction of the sagittal and lambdoidal sutures. 

Occipital Point. The point in the middle line of the occipital bone farthest from the glabella. 

Inion. The external occipital protuberance. 

Opisthion. The mid-point of the posterior margin of the foramen magnum. 

Basion. The mid-point of the anterior margin of the foramen magnum. 

The Points on Either Side of the Median Plane are the: 

Gonion. The outer margin of the angle of the mandible. 

Dacryon. The point of union of the antero-superior angle of the lacrimal with the frontal 
bone and the frontal process of the maxilla. 

Stephanion. The point where the temporal line intersects the coronal suture. 

Pterion. The point where the great wing of the sphenoid joins the sphenoidal angle of the 
parietal. 

Auricular Point. The center of the orifice of the external acoustic meatus. 

Asterion. The point of meeting of the lambdoidal, mastociccipital, and mastoparietal sutures. 

The horizontal circumference of the cranium is measured in a plane passing through the glabella 
(Turner) or the ophryon (Flower) in front, and the occipital point behind; it averages about 
50 cm. in the female and 52.5 cm. in the male. 

The occipitofrontal or longitudinal arc is measured from the nasion over the middle line of the 
vertex to the opisthion: while the basinasal length is the distance between the basion and the 
nasion. These two measurements, plus the antero-posterior diameter of the foramen magnum, 
represent the vertical circumference of the cranium. 

The length is measured from the glabella to the occipital point, while the breadth or greatest 

transverse diameter is usually found near the external acoustic meatus. The proportion of 

. 1 ,. , T. (breadth X 100) . 

breadth to length . -r^ is termed the cephalic index or i?idex of breadth. 

The height is usually measured from the basion to the bregma, and the proportion of height 

^ (height X 100) 
to length . ,, constitutes the vertical or height index. 

In studjing the face the principal points to be noticed are the proportion of its length and 
breadth, the shape of the orbits and of the anterior nasal aperture, and the degree of projection 
of the jaws. 

The length of the face may be measured from the ophryon or nasion to the chin, or, if the mandible 
be wanting, to the alveolar point; while its width is represented by the distance between the 
zygomatic arches. By comparing the length with the width of the face, skulls may be divided 
into two groups; dolichofacial or leptoprosope (long faced) and brachyfacial or chemoprosope (short 
faced). 

The orbital index signifies the proportion which the orbital height bears to the orbital width, 
thus: 

orbital height X 100 
orbital width 
The nasal index expresses the proportion which the width of the anterior nasal aperture bears 
to the height of the nose, the latter being measured from the nasion to the lower margin of the 
nasal aperture, thus: 

nasal width X 100 
nasal height 



CRANIOLOGY 



199 



The degree of projection of the jaws is determined by the gnathic or aheolar index, which repre- 
sents the proportion between the basialvcolar and basinasal lengths, thus: 

basialveolar length X 100 
basinasal length 
The following table, modified from that given by Duckworth,' illustrates how these different 
indices may be utihzed in the classification of skulls: 



Index. 


Classification. 


Nomenclature. 


Examples. 


1. Cephalic 


Below 75 

Between 75 and 80 
Above 80 

Below 84 

Between 84 and S9 
Above 89 


DoUchocephalic 

MesaticephaUc 

Brachycephalic 


Kaffirs and Native Australians. 
Europeans and Chinese. 
Mongohans and Andamans. 


2. Orbital 


Microseme 

Mesoseme 
Megaseme 

Leptorhine 
Mesorhine 
Platyrhine 

Orthognathous 
Mesognathous 
Prognathous 


Tasmanians and Native Austra- 

Hans. 
Europeans. 
Chinese and Polynesians. 


3. Nasal 


Below 48 

Between 48 and 53 
Above 53 


Europeans. 

Japanese and Chinese. 

Negroes and Native Australians. 


4. Gnathic 


Below 98 

Between 98 and 103 

Above 103 


Europeans. 

Chinese and Japanese. 

Native Australians. 



The chief function of the skull is to protect the brain, and therefore those portions of the skull 
which are most exposed to external violence are thicker than those which are shielded from injury 
by overlying muscles. Thus, the skull-cap is thick and dense, whereas the temporal squamse 
being protected by the temporales muscles, and the inferior occipital fossae, being shielded by the 
muscles at the back of the neck, are thin and fragile. Fracture of the skull is further prevented 
by its elasticity, its rounded shape, and its construction of a number of secondary elastic arches, 
each made up of a single bone. The manner in which vibrations are transmitted through the 
bones of the skull is also of importance as regards its protective mechanism, at all events as far 
as the base is concerned. In the vault, the bones being of a fairly equal thickness and density, 
vibrations are transmitted in a uniform manner in all directions, but in the base, owing to the 
varying thickness and density of the bones, this is not so; and therefore in this situation there 
are special buttresses which serve to carry the vibrations in certain definite directions. At the 
front of the skull, on either side, is the ridge which separates the anterior from the middle fossa 
of the base; and behind, the ridge or buttress which separates the middle from the posterior fossa; 
and if any violence is apphed to the vault, the vibrations would be carried along these buttresses 
to the sella turcica, where they meet. This part has been termed the "center of resistance," 
and here there is a special protective mechanism to guard the brain. The subarachnoid cavity 
at the base of the brain is dilated, and the cerebrospinal fluid which fills it acts as a water cushion 
to shield the brain from injury. In like manner, when violence is applied to the base of the skull, 
as in falls upon the feet, the vibrations are carried backward through the occipital crest, and 
forward through the basilar part of the occipital and body of the sphenoid to the vault of the skull. 

In connection with the bones of the face a common malformation is cleft palate. The cleft 
usually starts posteriorly, and its most elementary form is a bifid uvula; or the cleft may extend 
through the soft palate; or the posterior part of the whole 
of the hard palate may be involved, the cleft extending as 
far forward as the incisive foramen. In the severest forms, 
the cleft extends through the alveolus and passes between 
the incisive or premaxillary bone and the rest of the max- 
iUa; that is to say, between the lateral incisor and canine 
teeth. In some instances, the cleft runs between the central 
and lateral incisor teeth; and this has induced some 
anatomists to believe that the premaxillary bone is devel- 
oped from two centers (Fig. 199) and not from one, as was 
stated on p. 163. The medial segment, bearing a central 
incisor, is called an endognathion; the lateral segment, bear- 
ing the lateral incisor, is called a mesognathion. The cleft 

may affect one or both sides; if the latter, the central part is frequently displaced forward and re- 
mains united to the septum of the nose, the deficiency in the alveolus being complicated with a cleft 

' Morphology and Anthropology, by W. L. H. Duckworth, M.A., Cambridge University Press. 



EndognatTiion 
Mesognathion j!:^ 
Exognath ion 




Fig. 199. — The premaxilla and its sutures. 
(After Albrecht.) 



200 OSTEOLOGY 

in the lip (hare-lip). On examining a cleft palate in which the alveolus is not impHcated, the cleft 
will generally appear to be in the median line, but occasionally is unilateral and in some cases bilat- 
eral. To understand this it must be bornein mind that three processes are concerned in the formation 
of the palate — the palatine processes of the two maxillte, which grow in horizontally and unite 
in the middle line, and the ethmovomerine process, which grows downward from the base of 
the skull and frontonasal process to unite with the palatine processes in the middle line. In 
those cases where the palatine processes fail to unite with each other and with the medial process, 
the cleft of the palate is median; where one palatine process unites with the medial septum, the 
other faihng to do so, the cleft in the palate is unilateral. In some cases where the palatine pro- 
cesses fail to meet in the middle, the ethmovomerine process grows downward between them and 
thus produces a bilateral cleft. Occasionally there may be a hole in the middle line of the hard 
palate, the anterior part of the hard and the soft palate being perfect; this is rare, because, as 
a rule, the union of the various processes progresses from before backward, and therefore the 
posterior part of the palate is more frequently defective than the anterior. 

THE EXTREMITIES. 

The bones by which the upper and lower limbs are attached to the trunk con- 
stitute respectively the shoulder and pelvic girdles. The shoulder girdle or girdle 
of the superior extremity is formed by the scapulae and clavicles, and is imperfect 
in front and behind. In front, however, it is completed by the upper end of the 
sternum, with which the medial ends of the clavicles articulate. Behind, it is 
widely imperfect, the scapulae being connected to the trunk by muscles only. 
The pelvic girdle or girdle of the inferior extremity is formed by the hip bones, 
which articulate with each other in front, at the symphysis pubis. It is imperfect 
behind, but the gap is filled in by the upper part of the sacrum. The pelvic girdle, 
with the sacrum, is a complete ring, massive and comparatively rigid, in marked 
contrast to the lightness and mobility of the shoulder girdle. 

THE BONES OF THE UPPER EXTREMITY (OSS A EXTREMITATIS SUPERIORIS). 

The Clavicle (Clavicula; Collar Bone). 

The clavicle (Figs. 200, 201) forms the anterior portion of the shoulder girdle. 
It is a long bone, curved somewhat like the italic letter/, and placed nearly horizon- 
tally at the upper and anterior part of the thorax, immediately above the first 
rib. It articulates medially with the manubrium sterni, and laterally with the 
acromion of the scapula.^ It presents a double curvature, the convexity being 
directed forward at the sternal end, and the concavity at the scapular end. Its 
lateral third is flattened from above downward, while its medial two-thirds is of 
a rounded or prismatic form. 

Lateral Third. — The lateral third has two surfaces, an upper and a lower; and 
two borders, an anterior and a posterior. 

Surface. — The upper surface is flat, rough, and marked by impressions for the 
attachments of the Deltoideus in front, and the Trapezius behind; between these 
impressions a small portion of the bone is subcutaneous. The imder surface is 
flat. At its posterior border, near the point where the prismatic joins with the 
flattened portion, is a rough eminence, the coracoid tuberosity (conoid tubercle); 
this, in the natural position of the bone, surmounts the coracoid process of the 
scapula, and gives attachment to the conoid ligament. From this tuberosity an 
oblique ridge, the oblique or trapezoid ridge, runs forward and lateralward, and 
aftord attachment to the trapezoid ligament. 

1 The clavicle acts especially as a fulcrum to enable the muscles to give lateral motion to the arm. It is accordingly 
absent in those animals whose fore-limbs are used only for progression, but is present for the most part in animals 
whose anterior extremities are clawed and used for prehension, though in some of them — as, for instance, in a large 
number of the carnivora — it is merely a rudimentarj' bone suspended among the muscles, and not articulating with 
either the scapula or sternum. 



THE CLAVICLE 



201 



Borders. — The anterior border is concave, thin, and rough, and gives attachment 
to the Deltoideus. The posterior border is convex, rough, thicker than the anterior, 
and gives attachment to the Trapezius. 

Medial Two-thirds.— The medial two-thirds constitute the prismatic portion 
of the bone, which is curved so as to be convex in front, concave behind, and is 
marked by three borders, separating three surfaces. 

Borders. — The anterior border is continuous with the anterior margin of the fiat 
portion. Its lateral part is smooth, and corresponds to the interval between the 
attachments of the Pectoralis major and Deltoideus; its medial part forms the 
lower boundary of an elliptical surface for the attachment of the clavicular portion 



Sternal extremity 



Acromial extremity 




Fig. 200. — Left clavicle. Superior surface. 

of the Pectoralis major, and approaches the posterior border of the bone. The 
superior border is continuous with the posterior margin of the flat portion, and 
separates the anterior from the posterior surface. Smooth and rounded laterally, 
it becomes rough toward the medial third for the attachment of the Sternocleido- 
mastoideus, and ends at the upper angle of the sternal extremity. The posterior 
or subclavian border separates the posterior from the inferior surface, and extends 
from the coracoid tuberosity to the costal tuberosity; it forms the posterior bouii- 
dary of the groove for the Subclavius, and gives attachment to a layer of cervical 
fascia which envelops the Omohyoideus. 



Articular capsule 



Articular capsule 




Fio. 201. — Left clavicle. Inferior surface. 



Surfaces. — The anterior surface is included between the superior and anterior 
borders. Its lateral part looks upward, and is continuous with the superior sur- 
face of the flattened portion; it is smooth, convex, and nearly subcutaneous, being 
covered only by the Platysma. Medially it is divided by a narrow subcutaneous 
area into two parts: a lower, elliptical in form, and directed forward, for the 
attachment of the Pectoralis major; and an upper for the attachment of the 
Sternocleidomastoideus. The posterior or cervical surface is smooth, and looks 
backward toward the root of the neck. It is limited, above, by the superior 
border; below, by the subclavian border; medially, by the margin of the sternal 
extremity; and laterally, by the coracoid tuberosity. It is concave medio-laterally, 



202 OSTEOLOGY 

and is in relation, by its lower part, with the transverse scapular vessels. This 
surface, at the junction of the curves of the bone, is also in relation with the brachial 
plexus of nerves and the subclavian vessels. It gives attachment, near the sternal 
extremity, to part of the Sternohyoideus ; and presents, near the middle, an oblique 
foramen directed lateralward, which transmits the chief nutrient artery of the 
bone. Sometimes there are two foramina on the posterior surface, or one on the 
posterior and another on the inferior surface. The inferior or subclavian surface is 
bounded, in front, by the anterior border; behind, by the subclavian border. 
It is narrowed medially, but gradually increases in width laterally, and is contin- 
uous with the imder surface of the flat portion. On its medial part is a broad 
rough surface, the costal tuberosity {rhomboid impression), rather more than 2 cm. 
in length, for the attachment of the costoclavicular ligament. The rest of this 
surface is occupied by a groove, which gives attachment to the Subclavius; the 
coracoclavicular fascia, which splits to enclose the muscle, is attached to the margins 
of the groove. Not infrequently this groove is subdi\ided longitudinally by a 
line which gives attachment to the intermuscular septum of the Subclavius. 

The Sternal Extremity {extremiias sternalis; internal extremity). — The sternal 
extremity of the clavicle is triangular in form, directed medialward, and a little 
downward and forward; it presents an articular facet, concave from before back- 
ward, convex from above downward, which articulates with the manubrium sterni 
through the intervention of an articular disk. The lower part of the facet is con- 
tinued on to the inferior surface of the bone as a small semi-oval area for articula- 
tion with the cartilage of the first rib. The circumference of the articular surface 
is rough, for the attachment of numerous ligaments; the upper angle gives attach- 
ment to the articular disk. 

The Acromial Extremity (extremitas acromialis; aider extremity). — The acromial 
extremity presents a small, flattened, oval surface directed obliquely downward, 
fgr articulation with the acromion of the scapula. The circiunference of the 
articular facet is rough, especially above, for the attachment of the acromio- 
clavicular ligaments. 

In the female, the clavicle is generally shorter, thinner, less curved, and smoother than in the 
male. In those persons who perform considerable manual labor it becomes thicker and more 
curved, and its ridges for muscular attachment are prominently marked. 

Structure. — The clavicle consists of cajicellous tissue, enveloped by a compact laj-er, which 
is much thicker in the intermediate part than at the extremities of the bone. 

Ossification. — The clavicle begins to ossify before any other bone in the body; it is ossified 
from three centers — viz., two primary centers, a medial and a lateral, for the body,* which appear 
during the fifth or sixth week of fetal hfe; and a secondarj- center for the sternal end, which 
appears about the eighteenth or twentieth year, and unites with the rest of the bone about the 
twenty-fifth year. 

The Scapula i, Shoulder Blade). 

The scapula forms the posterior part of the shoulder girdle. It is a flat, trian- 
gular bone, with two surfaces, three borders, and three angles. 

Surfaces. — The costal or ventral surface (Fig. 202) presents a broad concavity, 
the subscapular fossa. The medial two-thirds of the fossa are marked by several 
oblique ridges, which run lateralward and upward. The ridges give attachment 
to the tendinous insertions, and the surfaces between them to the fleshy fibers, 
of the Subscapularis. The lateral third of the fossa is smooth and coA-ered by the 
fibers of this muscle. The fossa is separated from the vertebral border by smooth 
triangular areas at the medial and inferior angles, and in the interval between 
these by a narrow ridge which is often deficient. These triangular areas and the 
intervening ridge afford attachment to the Serratus anterior. At the upper part 
of the fossa is a transverse depression, where the bone appears to be bent on itself 

1 Mall, American Journal of Anatomy, vol. v; Fawcett, Journal of Anatomy and Physiologj-, vol. slvii. 



THE SCAPULA 203 

along a line at right angles to and passing through the center of the glenoid cavity, 
forming a considerable angle, called the subscapular angle; this gives greater 
strength to the body of the bone by its arched form, while the summit of the 
arch serves to support the spine and acromion. 

The dorsal surface (Fig. 203) is arched from above downward, and is subdivided 
into two unequal parts by the spine; the portion above the spine is called the 
supraspinatous fossa, and that below it the infraspinatous fossa. 

The supraspinatous fossa, the smaller of the two, is concave, smooth, and broader 
at its vertebral than at its humeral end; its medial two-thirds give origin to the 
Supraspinatus. 

The infraspinatous fossa is much larger than the preceding; toward its vertebral 
margin a shallow concavity is seen at its upper part; its center presents a promi- 
nent convexity, while near the axillary border is a deep groove which runs from 
the upper toward the lower part. The medial two-thirds of the fossa give origin 
to the Infraspinatus; the lateral third is covered by this muscle. 

The dorsal surface is marked near the axillary border by an elevated ridge, 
which runs from the lower part of the glenoid cavity, downward and backward 
to the vertebral border, about 2.5 cm. above the inferior angle. The ridge serves 
for the attachment of a fibrous septum, which separates the Infraspinatus from 
the Teres major and Teres minor. The surface between the ridge and the axillary 
border is narrow in the upper two-thirds of its extent, and is crossed near its 
center by a groove for the passage of the scapular circumflex vessels; it affords 
attachment to the Teres minor. Its lower third presents a broader, somewhat 
triangular surface, which gives origin to the Teres major, and over which the Latis- 
simus dorsi glides; frequently the latter muscle takes origin by a few fibers from 
this part. The broad and narrow portions above alluded to are separated by an 
oblique line, which runs from the axillary border, downward and backward, to 
meet the elevated ridge: to it is attached a fibrous septum which separates the 
Teres muscles from each other. 

The Spine (spina scapulw). — The spine is a prominent plate of bone, which 
crosses obliquely the medial four-fifths of the dorsal surface of the scapula at its 
upper part, and separates the supra- from the infraspinatous fossa. It begins 
at the vertical border by a smooth, triangular area over which the tendon of inser- 
tion of the lower part of the Trapezius glides, and, gradually becoming more ele- 
vated, ends in the acromion, which overhangs the shoulder-joint. The spine is 
triangular, and flattened from above downward, its apex being directed toward 
the vertebral border. It presents two surfaces and three borders. Its superior 
surface is concave; it assits in forming the supraspinatous fossa, and gives origin 
to part of the Supraspinatus. Its inferior surface forms part of the infraspinatous 
fossa, gives origin to a portion of the Infraspinatus, and presents near its center 
the orifice of a nutrient canal. Of the three borders, the anterior is attached to the 
dorsal surface of the bone; the posterior, or crest of the spine, is broad, and presents 
two lips and an intervening rough interval. The Trapezhis is attached to the supe- 
rior lip, and a rough tubercle is generally seen on that portion of the spine which 
receives the tendon of insertion of the lower part of this muscle. The Deltoideus 
is attached to the whole length of the inferior lip. The interval between the lips 
is subcutaneous and partly covered by the tendinous fibers of these muscles. The 
lateral border, or base, the shortest of the three, is slightly concave; its edge, thick 
and round, is continuous above with the under surface of the acromion, below 
with the neck of the scapula. It forms the medial boundary of the great scapular 
notch, which serves to connect the supra- and infraspinatous fossae. 

The Acromion.^The acromion forms the summit of the shoulder, and is a large, 
somewhat triangular or oblong process, flattened from behind forward, projecting 
at first lateralward, and then curving forward and upward, so as to overhang the 



204 



OSTEOLOGY 



glenoid cavity. Its superior surface, directed upward, backward, and lateralward, 
is convex, rough, and gives attachment to some fibers of the Deltoideus, and in the 
rest of its extent is subcutaneous. Its inferior surface is smooth and concave. 
Its lateral border is thick and irregular, and presents three or four tubercles for the 
tendinous origins of the Deltoideus. Its medial border, shorter than the lateral, 
is concave, gives attachment to a portion of the Trapezius, and presents about 
its center a small, oval surface for articulation with the acromial end of the clavicle. 



Articrdar capsule 



Cora coacromial 
ligament 



Articular 
capsule 




FiQ. 202. — Left scapula. Costal surface. 



Its apex, which corresponds to the point of meeting of these two borders in front, 
is thin, and has attached to it the coracoacromial ligament. 

Borders.— Of the three borders of the scapula, the superior is the shortest and 
thinnest; it is concave, and extends from the medial angle to the base of the cora- 
coid process. At its lateral part is a deep, semicircular notch, the scapular notch, 



THE SCAPULA 



205 



formed partly by the base of the coracoid process. This notch is converted into 
a foramen by the superior transverse ligament, and serves for the passage of the 
suprascapular nerve; sometimes the ligament is ossified. The adjacent part of 
the superior border affords attachment to the Omohyoideus. The axillary border 



Coracohumeral 
ligament 



Coraco-acromial ligament 



^'^fo 



Trapezoid ligament 



Conoid ligament 



Articvlar 
capsule 




Fia. 203. — Left scapula. Dorsal surface. 



is the thickest of the three. It begins above at the lower margin of the glenoid 
cavity, and inclines obliquely downward and backward to the inferior angle. 
Immediately below the glenoid cavity is a rough impression, the infraglenoid 
tuberosity, about 2.5 cm. in length, which gives origin to the long head of the Tri- 
ceps brachii; in front of this is a longitudinal groove, which extends as far as the 



206 



OSTEOLOGY 



lower third of this border, and affords origin to part of the Subscapularis. The 
inferior third is thin and sharp, and serves for the attachment of a few fibers of 
the Teres major behind, and of the Subscapularis in front. The vertebral border 
is the longest of the three, and extends from the medial to the inferior angle. It 
is arched, intermediate in thickness between the superior and the axillary borders, 
and the portion of it above the spine forms an obtuse angle with the part below. 
This border presents an anterior and a posterior lip, and an intermediate narrow 
area. The anterior lip affords attachment to the Serratus anterior; the posterior 
lip, to the Supraspinatus above the spine, the Infraspinatus below; the area 




Fig. 204. — Posterior view of the thorax and shoulder girdle. (Morris.) 



between the two lips, to the Levator scapula* above the triangular surface at the 
commencement of the spine, to the Rhomboideus minor on the edge of that surface, 
and to the Rhomboideus major below it; this last is attached by means of a fibrous 
arch, connected above to the lower part of the triangular surface at the base of 
the spine, and below to the lower part of the border. 

Angles. — Of the three angles, the medial, formed by the junction of the superior 
and vertebral borders, is thin, smooth, rounded, inclined somewhat lateralward, 
and gives attachment to a few fibers of the Levator scapulae. The inferior angle, 
thick and rough, is formed by the union of the vertebral and axillary borders; 
its dorsal surface affords attachment to the Teres major and frequently to a few 



THE SCAPULA 



207 



Coracoid 
process 



Acromion 



Glenoid cavity 



Infraglenoid tubercle 



fibers of the Latissimus dorsi. The lateral angle is the thickest part of the bone, 
and is sometimes called the head of the scapula. On it is a shallow pvriform, 
articular surface, the glenoid cavity, which is directed lateralward and 'forward 
and articulates with the head of the humerus; it is broader below than above 
and its vertical diameter is the longest. The surface is covered with cartilage 
in the fresh state; and its margins, slightly raised, give attachment to a fibro- 
cartilaginous structure, the glenoidal labrum, which deepens the cavity. At its 
apex is a slight elevation, the 

SUpraglenoid tuberosity, to which Supraglenoid tubercle 

the long head of the Biceps 
brachii is attached. The neck 
of the scapula is the slightly 
constricted portion which sur- 
rounds the head; it is more dis- 
tinct below and behind than 
above and in front. 

The Coracoid Process (processus 
coracoideus) . — The coracoid pro- 
cess is a thick curved process at- 
tached bv a broad base to the 
upper part of the neck of the 
scapula; it runs at first upward 
and medialward; then, becoming 
smaller, it changes its direction, 
and projects forward and lateral- 
ward. The ascending portion, 
flattened from before backward, 
presents in front a smooth con- 
cave surface, across which the 
Subscapularis passes. The hori- 
zontal portion is flattened from 
above downward; its upper sur- 
face is convex and irregular, and 
gives attachment to the Pector- 
alis minor; its under surface is 
smooth; its medial and lateral 
borders are rough; the former 
gives attachment to the Pectoralis 
minor and the latter to the cora- 
coacromial ligament; the apex is 
embraced by the conjoined tendon 
of origin of the Coracobrachialis 
and short head of the Biceps 
brachii and gives attachment to 
the coracoclavicular fascia. On 
the medial part of the root of the 
coracoid process is a rough im- 
pression for the attachment of 
the conoid ligament; and running from it obliquely forward and lateralward, 
on to the upper. surface of the horizontal portion, is an elevated ridge for the 
attachment of the trapezoid ligament. 




For Subscapularis 



Axillary border 




-Inferior arujle 
Fig. 205. — Left scapula. Lateral view. 



Structure.^The head, processes, and the thickened parts of the bone, contain cancellous 
tissue; the rest consists of a thin layer of compact tissue. The central part of the supraspinatous 



208 



OSTEOLOGY 



fossa and the upper part of the infraspinatous fossa, but especially the former, are usually so thin 
as to be semitransparent; occasionally the bone is found wanting in this situation, and the adjacent 
muscles are separated only by fibrous tissue. 

Ossification (Fig. 206). — The scapula is ossified from seven or more centers: one for the body, 
two for the coracoid process, two for the acromion, one for the vertebral border, and one for the 
inferior angle. 

Ossification of the body begins about the second month of fetal life, by the formation of an 
irregular quadrilateral plate of bone, immediately behind the glenoid cavity. This plate extends 
so as to form the chief part of the bone, the spine growing up from its dorsal surface about the 
third month. At birth, a large part of the scapula is osseous, but the glenoid cavity, the coracoid 
process, the acromion, the vertebral border, and the inferior angle are cartilaginous. From the 
fifteenth to the eighteenth month after birth, ossification takes place in the middle of the coracoid 
process, which as a rule becomes joined with the rest of the bone about the fifteenth year. Between 
the fourteenth and twentieth years, ossification of the remaining parts takes place in quick succes- 
sion, and usually in the following order; first, in the root of the coracoid process, in the form of a 
broad scale; secondly, near the base of the acromion; thirdly, in the inferior angle and contiguous 
part of the vertebral border; fourthly, near the extremity of the acromion; fifthly, in the vertebral 
border. The base of the acromion is formed by an extension from the spine; the two separate 
nuclei of the acromion unite, and then join with the extension from the spine. The upper third 




Fig. 206. — Plan of ossification of the scapula. From seven centers. 



of the glenoid cavity is ossified from a separate center (subcoracoid), which makes its appear- 
ance between the tenth and eleventh years and joins between the sixteenth and the eighteenth. 
Further, an epiphysial plate appears for the lower part of the glenoid cavity, while the tip of the 
coracoid process frequently presents a separate nucleus. These various epiphyses are joined 
to the bone by the twenty-fifth year. Failure of bony union between the acromion and spine 
sometimes occurs, the junction being effected by fibrous tissue, or by an imperfect articulation; 
in some cases of supposed fracture of the acromion with ligamentous union, it is probable that 
the detached segment was never united to the rest of the bone. 



THE HUMERUS 209 



The Humerus (Arm Bone). 

The humerus (Figs. 207, 208) is the longest and largest bone of the upper 
extremity; it is divisible into a body and two extremities. 

Upper Extremity.— The upper extremity consists of a large rounded head joined 
to the body by a constricted portion called the neck, and two eminences, the greater 
and lesser tubercles. 

The Head {cayut humeri).— The head, nearly hemispherical in form,i is directed 
upward, medial ward, and a little backward, and articulates with the glenoid cavity 
of the scapula. The circumference of its articular surface is slightly constricted 
and is termed the anatomical neck, in contradistinction to a constriction below the 
tubercles called the surgical neck which is frequently the seat of fracture. Fracture 
of the anatomical neck rarely occurs. 

The Anatomical Neck (collum anatomicum) is obliquely directed, forming an 
obtuse angle with the body. It is best marked in the lower half of its circum- 
ference ; in the upper half it is represented by a narrow groove separating the head 
from the tubercles. It affords attachment to the articular capsule of the shoulder- 
joint, and is perforated by numerous vascular foramina. 

The Greater Tubercle (tuberculum majus; greater tuberosity). — The greater 
tubercle is situated lateral to the head and lesser tubercle. Its upper surface is 
rounded and marked by three flat impressions : the highest of these gives insertion 
to the Supraspinatus; the middle to the Infraspinatus; the lowest one, and the 
body of the bone for about 2.5 cm. below it, to the Teres minor. The lateral 
surface of the greater tubercle is convex, rough, and continuous with the lateral 
surface of the body. 

The Lesser Tubercle {tuberculum minus; lesser tuberosity). — The lesser tubercle, 
although smaller, is more prominent than the greater: it is situated in front, and 
is directed medialward and forward. Above and in front it presents an impression 
for the insertion of the tendon of the Subscapularis. 

The tubercles are separated from each other by a deep groove, the intertubercular 
groove (bicipital groove), which lodges the long tendon of the Biceps brachii and 
transmits a branch of the anterior humeral circumflex artery to the shoulder-joint. 
It runs obliquely downward, and ends near the junction of the upper with the 
middle third of the bone. In the fresh state its upper part is covered with a 
thin layer of cartilage, lined by a prolongation of the synovial membrane of the 
shoulder-joint; its lower portion gives insertion to the tendon of the Latissimus 
dorsi. It is deep and narrow above, and becomes shallow and a little broader 
as it descends. Its lips are called, respectively, the crests of the greater and lesser 
tubercles {bicipital ridges), and form the upper parts of the anterior and medial 
borders of the body of the bone. 

The Body or Shaft {corpus humeri). — The body is almost cylindrical in the upper 
half of its extent, prismatic and flattened below, and has three borders and three 
surfaces. 

Borders. — The anterior border runs from the front of the greater tubercle above 
to the coronoid fossa below, separating the antero-medial from the antero-lateral 
surface. Its upper part is a prominent ridge, the crest of the greater tubercle; 
it serves for the insertion of the tendon of the Pectoralis major. About its center 
it forms the anterior boundary of the deltoid tuberosity ; below, it is smooth and 
rounded, affording attachment to the Brachialis. 

The lateral border runs from the back part of the greater tubercle to the 

1 Though the head is nearly hemispherical in form, its margin, as Humphry has shown, is by no ineans a true circle. 
Its greatest diameter is, from the top of the intertubercular groove in a direction downward, medialward, and back- 
ward. Hence it follows that the greatest elevation of the arm can be obtained by rolling the articular surface m this 
direction — that is to say, obliquely upward, lateralward, and forward. 

14 



210 



OSTEOLOGY 
Articular capstde 



cavity 



^^ 



'.> ±<> 



^erc^ 



>' 



>Rl! 



L^'.^x. 



SurqCoai Neek- 






r- 

^ 



All; 

l"^ •-/ 



■ 'IJI 



V - 



\\ 



% 



oy 



•\5J 



Brachioradialis 



^ i^\ 



,m\^ 



Extensor carpi radialis 
longiLs 



Common origin oj 
Flexor carpi radialis '^% 
Palmaris longus '^'^ 

Flexor digitorum, svblimis 
Flexor carpi ulnaris 



'., FossO 

rochlea-M 



A: \^ 



Jt Capii 



ami 

niv, 



%i Articular capstde 



"S' 



V^ 



Common origin of 

Extensor carpi rad. brev, 
,, digitorum communis 
,, dig it i qu int i prop. 
,, carpi ulnaris 

Supinator 



Fig. 207. — Left humerus. Anterior view. 



THE HUMERUS 



211 



lateral epicondyle, and separates the antero- 
lateral from the posterior surface. Its upper 
half is rounded and indistinctly marked, serv- 
ing for the attachment of the lower part of the 
insertion of the Teres minor, and below this 
giving origin to the lateral head of the Triceps 
brachii; its center is traversed by a broad but 
shallow oblique depression, the radial sulcus 
(muscnlospiral groove). Its lower part forms a 
prominent, rough margin, a little curved from 
behind forward, the lateral supracondylar ridge, 
which presents an anterior lip for the origin 
of the Brachioradialis above, and Extensor 
carpi radialis longus below, a posterior lip for 
the Triceps brachii, and an intermediate ridge 
for the attachment of the lateral intermuscu- 
lar septum. 

The medial border extends from the lesser 
tubercle to the medial epicondyle. Its upper 
third consists of a prominent ridge, the crest of 
the lesser tubercle, which gives insertion to the 
tendon of the Teres major. About its center 
is a slight impression for the insertion of the 
Coracobrachialis, and just below this is the 
entrance of the nutrient canal, directed down- 
ward; sometimes there is a second nutrient 
canal at the commencement of the radial sulcus. 
The inferior third of this border is raised into 
a slight ridge, the medial supracondylar ridge, 
which becomes very prominent below; it pre- 
sents an anterior lip for the origins of the 
Brachialis and Pronator teres, a posterior lip 
for the medial head of the Triceps brachii, 
and an intermediate ridge for the attachment 
of the medial intermuscular septum. 

Surfaces. — The antero-lateral surface is di- 
rected laterahvard above, where it is smooth, 
rounded, and covered by the Deltoideus; for- 
ward and laterahvard below, where it is slightly 
concave from above downward, and gives origin 
to part of the Brachialis. About the middle 
of this surface is a rough, triangular elevation, 
the deltoid tuberosity for the insertion of the 
Deltoideus; below this is the radial sulcus, 
directed obliquely from behind, forward, and 
downward, and transmitting the radial nerve 
and profunda artery. 

The antero-medial surface, less extensive than 
the antero-lateral, is directed medialward above, 
forward and medialw^ard below; its upper part 
is narrow, and forms the floor of the intertuber- 
cular groove which gives insertion to the tendon 
of the Latissimus dorsi; its middle part is 
slightly rough for the attachment of some of 



Uteres] 

>llt<OII 






f^\ 



t > 



toll 



Articular 
capsule 



Articvlar 
capsule 






\\ fffLt^^^* 



Fig. 208. — Left humerus Posterior view. 



212 OSTEOLOGY 

the fibers of the tendon of insertion of the Coracobrachialis; its lower part is 
smooth, concave from above downward, and gives origin to the Brachiahs.^ 

The posterior surface appears somewhat twisted, so that its upper part is 
directed a httle medialward, its lower part backward and a little lateralward. 
Nearly the whole of this surface is covered by the lateral and medial heads of 
the Triceps brachii, the former arising above, the latter below the radial 

sulcus. 

The Lower Extremity. — The lower extremity is flattened from before backward, 
and curved slightly forward; it ends below in a broad, articular surface, which is 
divided into two parts by a slight ridge. Projecting on either side are the lateral 
and medial epicondyles. The articular surface extends a little lower than the 
epicondyles, and is curved slightly forward ; its medial extremity occupies a lower 
level than the lateral. The lateral portion of this surface consists of a smooth, 
rounded eminence, named the capitulum of the humerus ; it articulates with the cup- 
shaped depression on the head of the radius, and is limited to the front and lower 
part of the bone. On the medial side of this eminence is a shallow groove, in which 
is received the medial margin of the head of the radius. Above the front part 
of the capitulum is a slight depression, the radial fossa, which receives the anterior 
border of the head of the radius, when the forearm is flexed. The medial portion 
of the articular surface is named the trochlea, and presents a deep depression be- 
tween two well-marked borders; it is convex from before backward, concave from 
side to side, and occupies the anterior, lower, and posterior parts of the extremity. 
The lateral border separates it from the groove which articulates with the margin 
of the head of the radius. The medial border is thicker, of greater length, and 
consequently more prominent, than the lateral. The grooved portion of the artic- 
ular surface fits accurately within the semilunar notch of the ulna; it is broader and 
deeper on the posterior than on the anterior aspect of the bone, and is inclined 
obliquely downward and forward toward the medial side. Above the front part 
of the trochlea is a small depression, the coronoid fossa, which receives the coronoid 
process of the ulna during flexion of the forearm. Above the back part of the troch- 
lea is a deep triangular depression, the olecranon fossa, in which the summit of the 
olecranon is received in extension of the forearm. These fossae are separated from 
one another by a thin, transparent lamina of bone, which is sometimes perforated 
by a supratrochlear foramen; they are lined in the fresh state by the synovial 
membrane of the elbow-joint, and their margins afford attachment to the anterior 
and posterior ligaments of this articulation. The lateral epicondyle is a small, 
tuberculated eminence, curved a little forward, and giving attachment to the radial 
collateral ligament of the elbow-joint, and to a tendon common to the origin of 
the Supinator and some of the Extensor muscles. The medial epicondyle, larger 
and more prominent than the lateral, is directed a little backward ; it gives attach- 
ment to the ulnar collateral ligament of the elbow-joint, to the Pronator teres, 
and to a common tendon of origin of some of the Flexor muscles of the forearm; 
the ulnar nerve runs in a groove on the back of this epicondyle. The epicondyles 
are continuous above with the supracondylar ridges. 

Structure. — The extremities consist of cancellous tissue, covered with a thin, compact layer 
(Fig. 209) ; the body is composed of a cylinder of compact tissue, thicker at the center than toward 
the extremities, and contains a large medullary canal which extends along its whole length. 

1 A small, hook-shaped process of bone, the supracondylar process, varying from 2 to 20 mm. in length, is not infre- 
quently found projecting from the antero-medial surface of the body of the humerus 5 cm. above the medial epicondyle. 
It is curved downward and forward, and its pointed end is connected to the medial border, just above the medial 
epicondyle, by a fibrous band, which gives origin to a portion of the Pronator teres; through the arch completed by 
this fibrous band the median nerve and brachial artery pass, when these structures deviate from their usual course. 
Sometimes the nerve alone is transmitted through it, or the nerve may be accompanied by the ulnar artery, in cases 
of high division of the brachial. A well-marked groove is usually found behind the process, in which the nerve and 
artery are lodged. This arch is the homologue of the supracondyloid foramen found in many animals, and probably 
Berves in them to protect the nerve and artery from compression during the contraction of the muscles in this region. 



THE HUMERUS 



213 



Ossification (Figs. 210, 211).— The humerus is ossi- 
fied from eight centers, one for each of the following 
parts; the body, the head, the greater tubercle, the 
lesser tubercle, the capitulum, the trochlea, and one 
for each epicondyle. The center for the body appears 
near the middle of the bone in the eighth week of fetal 
fife, and soon extends toward the extremities. At birth 
the humerus is ossified in nearly its whole length, only 
the extremities remaining cartilaginous. During the 
first year, sometimes before birth, ossification commences 
in the head of the bone, and dm-ing the third year the 
center for the greater tubercle, and during the fifth that 
for the lesser tubercle, make their appearance. By the 
sixth year the centers for the head and tubercles have 
joined, so as to form a single large epiphysis, which fuses 
with the body about the twentieth year. The lower end 
of the humerus is ossified as follows. At the end of 
the second year ossification begins in the capitulum, 
and extends medialward, to form the chief part of the 
articular end of the bone; the center for the medial part 
of the trochlea appears about the age of twelve. Ossifi- 
cation begins in the medial epicondyle about the fifth 
year, and in the lateral about the thirteenth or four- 
teenth year. About the sixteenth or seventeenth year, 
the lateral epicondyle and both portions of the articu- 
lating surface, having already joined, unite with the 
body, and at the eighteenth year the medial epicon- 
dyle becomes joined to it. 



Epiphysial line 




Fig. 209. — Longitudinal section of head of 
left humerus. 



Epiphyses of head and 
tubercles blend at fifth 
year, and unite with 
body at twentieth 
year 



Unites with body\ 
at ei<jhitenth year) t^" 




Blcn3. O'f^ a\ ^^ 





Fig. 210. — Plan of ossification of the humerus. 



Fig. 211. — Epiphysial lines of humerus in a young 
adult. Anterior aspect. The lines of attachment of 
the articular capsules are in blue. 



214 



OSTEOLOGY 



Olecranon 



The Ulna (Elbow Bone).i 

The ulna (Figs. 212, 213) is a long bone, prismatic in form, placed at the medial 
side of the forearm, parallel with the radius. It is divisible into a body and 
two extremities. Its upper extremity, of great thickness and strength, forms 
a large part of the elbow-joint; the bone diminishes in size from above downward, 

its lower extremity being very small, and excluded 
from the wrist-joint by the interposition of an 
articular disk. 

The Upper Extremity (proximal extremity) (Fig. 
212). — The upper extremity presents two curved 
processes, the olecranon and the coronoid process; 
and two concave, articular cavities, the semilunar 
and radial notches. 

The Olecranon [olecranon process). — The olecra- 
non is a large, thick, curved eminence, situated 
at the upper and back part of the ulna. It is bent 
forward at the summit so as to present a promi- 
nent lip which is received into the olecranon fossa 
of the himierus in extension of the forearm. Its 
base is contracted where it joins the body and the 
narrowest part of the upper end of the ulna. Its 
posterior surface, directed backward, is triangular, 
smooth, subcutaneous, and covered by a bursa. 
Its superior surface is of quadrilateral form, marked 
behind by a rough impression for the insertion of 
the Triceps brachii; and in front, near the margin, 
by a slight transverse groove for the attachment 
of part of the posterior ligament of the elbow -joint. 
Its anterior surface is smooth, concave, and forms 
the upper part of the semilunar notch. Its borders 
present continuations of the groove on the margin 
of the superior surface ; they serve for the attach- 
ment of ligaments, viz., the back part of the ulnar 
collateral ligament medially, and the posterior 
ligament laterally. From the medial border a part 
of the Flexor carpi ulnaris arises; while to the 
lateral border the Anconseus is attached. 

The Coronoid Process (processus coronoideus) . — 
The coronoid process is a triangular eminence 
projecting forward from the upper and front part 
of the ulna. Its base is continuous with the body 
of the bone, and of considerable strength. Its 
apex is pointed, slightly curved upward, and in 
flexion of the forearm is received into the coronoid 
fossa of the humerus. Its upper surface is smooth, concave, and forms the lower 
part of the semilunar notch. Its antero-inferior surface is concave, and marked by 
a rough impression for the insertion of the Brachialis. At the junction of this 
surface with the front of the body is a rough eminence, the tuberosity of the ulna, 
which gives insertion to a part of the Brachialis; to the lateral border of this 
tuberosity the oblique cord is attached. Its lateral surface presents a narrow, 
oblong, articular depression, the radial notch. Its medial surface, by its prominent, 




Fia. 212. — Upper extremity of left ulna. 
Lateral aspect. 



' In the anatomical position, the forearm is placed in extension and supination with the palm looking forward 
and the thumb on the outer side. 



THE ULNA 215 

free margin, serves for the attachment of part of the ulnar collateral ligament. 
At the front part of this surface is a small rounded eminence for the origin 
of one head of the Flexor digitorum sublimis; behind the eminence is a depression 
for part of the origin of the Flexor digitorum profundus; descending from the 
eminence is a ridge which gives origin to one head of the Pronator teres. Fre- 
quently, the Flexor pollicis longus arises from the lower part of the coronoid 
process by a rounded bundle of muscular fibers. 

The Semilunar Notch {incisiira semilunnris; greater sigmoid cavity). — The semi- 
lunar notch is a large depression, formed by the olecranon and the coronoid process, 
and serving for articulation with the trochlea of the humerus. About the middle 
of either side of this notch is an indentation, which contracts it somewhat, and 
indicates the junction of the olecranon and the coronoid process. The notch is 
concave from above downward, and divided into a medial and a lateral portion by 
a smooth ridge running from the summit of the olecranon to the tip of the coronoid 
process. The medial portion is the larger, and is slightly concave transversely; 
the lateral is convex above, slightly concave below. 

The Radial Notch {incisura radialis; lesser sigmoid cavity).— The radial notch 
is a narrow, oblong, articular depression on the lateral side of the coronoid process; 
it receives the circumferential articular surface of the head of the radius. It is 
concave from before backward, and its prominent extremities serve for the attach- 
ment of the annular ligament. 

The Body or Shaft {corpus idnce). — The body at its upper part is prismatic 
in form, and curved so as to be convex behind and lateralward; its central part 
is straight; its lower part is rounded, smooth, and bent a little lateralward. It 
tapers gradually from above downward, and has three borders and three surfaces. 

Borders. — The volar border {margo volaris; anterior border) begins above at the 
prominent medial angle of the coronoid process, and ends below in front of the 
styloid process. Its upper part, well-defined, and its middle portion, smooth and 
rounded, give origin to the Flexor digitorum profundus; its lower fourth serves 
for the origin of the Pronator quadratus. This border separates the volar from 
the medial surface. 

The dorsal border (margo dorsalis; posterior border) begins above at the apex of 
the triangular subcutaneous surface at the back part of the olecranon, and ends 
below at the back of the styloid process; it is well-marked in the upper three- 
fourths, and gives attachment to an aponeurosis which affords a common origin to 
the Flexor carpi ulnaris, the Extensor carpi ulnaris, and the Flexor digitorum pro- 
fundus; its lower fourth is smooth and rounded. This border separates the medial 
from the dorsal surface. 

The interosseous crest {crista interossea; external or interosseous border) begins 
above by the union of two lines, which converge from the extremities of the radial 
notch and enclose between them a triangular space for the origin of part of the 
Supinator; it ends below at the head of the ulna. Its upper part is sharp, its lower 
fourth smooth and rounded. This crest gives attachment to the interosseous mem- 
brane, and separates the volar from the dorsal surface. 

Surfaces. — The volar surface {fades volaris; anterior surface), much broader 
above than below, is concave in its upper three-fourths, and gives origin to the 
Flexor digitorum profundus; its lower fourth, also concave, is covered by the 
Pronator quadratus. The lower fourth is separated from the remaining portion 
by a ridge, directed obliquely downward and medialward, which marks the extent 
of origin of the Pronator quadratus. At the junction of the upper with the 
middle third of the bone is the nutrient canal, directed obliquely upward. 

The dorsal surface {fades dorsalis; posterior surface) directed backward and 
lateralward, is broad and concave above; convex and somewhat narrower in the 
middle; narrow, smooth, and rounded below. On its upper part is an oblique 



216 



OSTEOLOGY 



tTLNA 



Articular capsule 



BADIUS 



Flexor digitorum 
sublimis 



Pronator 

teres 

Occasional ori 
of Flexor ■pollicis lo 



Articular 
capsule 




\^ Radial origin of 
I Flexor digitorum 
I sublimis 



Styloid -process 



^"a^c&J^i^^^ 



Brack iorad ia lis 

Groove for Abductor 
pollicis longus and 
Extensor pollicis brevis 



Styloid process 
FiQ. 213. — Bones of left forearm. Anterior aspect. 



THE ULNA 



217 



ULNA 



For\ 



(Abductor pollicis 
I longus 

Extensor pollicis 
brevis 



RADIUS 



For Ext. carpi radialis longus 
For Extensor carpi radialis brevis 

For Extensor pollicis loiigus 




Articular capsule 



Flexor digitorum sublimis 



Articxdur capsule 



For Extensor carpi ^dnaris 
For Extensor digiti quinti proprius 



P (Extensor indicis proprius 
\Extensor digitorum comm 



communis 



Fia 214. — Bones of left forearm. Posterior aspect. 



218 



OSTEOLOGY 



ridge, which runs from the dorsal end of the radial notch, downward to the dorsal 
border; the triangular surface above this ridge receives the insertion of the 
Anconanis, while the upper part of the ridge affords attachment to the Supinator. 
Below this the surface is subdivided by a longitudinal ridge, sometimes called the 
perpendicular line, into two parts: the medial part is smooth, and covered by the 
Extensor carpi ulnaris; the lateral portion, wider and rougher, gives origin from 
above downward to the Supinator, the Abductor pollicis longus, the Extensor poUicis 
longus, and the Extensor indicis proprius. 

The medial surface {fades medialis; internal surface) is broad and concave 
above, narrow and convex below. Its upper three-fourths give origin to the 
Flexor digitorum profundus; its lower fourth is subcutaneous. 



Appears at 

tenth year 



Olecranon 

Joins body at 

sixteenth year 







Appears at 
fourth year 



Joins body at 
twentieth year 



Inferior extremity 




Fia. 



215. — Plan of ossification of the ulna. 
From three centers. 



Fig. 216. — Epiphysial lines of ulna in a young adult. 
Lateral aspect. The lines of attachment of the articular 
capsules are in blue. 



The Lower Extremity {distal extremity). — The lower extremity of the ulna is 
small, and presents two eminences; the lateral and larger is a rounded, articular 
eminence, termed the head of the ulna; the medial, narrower and more projecting, 
is a non-articular eminence, the styloid process. The head presents an articular 
surface, part of which, of an oval or semilunar form, is directed downward, and 
articulates with the upper surface of the triangular articular disk which separates it 
from the wrist-joint; the remaining portion, directed lateralward, is narrow, convex, 
and received into the ulnar notch of the radius. The styloid process projects from 
the medial and back part of the bone; it descends a little lower than the head, 
and its rounded end affords attachment to the ulnar collateral ligament of the 
wrist-joint. The head is separated from the styloid process by a depression for 
the attachment of the apex of the triangular articular disk, and behind, by a shallow 
groove for the tendon of the Extensor carpi ulnaris. 



THE RADIUS 219 

Structure.— The long, narrow medullary cavity is enclosed in a strong wall of compact tissue 
which is thickest along the interosseous border and dorsal surface. At the extremities the compact 
layer thins. The compact layer is continued onto the back of the olecranon as a plate of close 
spongy bone with lamella? parallel. From the inner surface of this plate and the compact layer 
below it trabecule arch forward toward the olecranon and coronoid and cross other trabecular, 
passing backward over the medullary cavity from the upper part of the shaft below the coronoid. 
Below the coronoid process there is a small area of compact bone from which trabecule curve 
upward to end obliquely to the surface of the semilunar notch which is coated with a thin layer of 
compact bone. The trabecular at the lower end have a more longitudinal direction. 

Ossification (Figs. 215, 216).— The ulna is ossified from three centers: one each for the body, the 
inferior extremity, and the top of the olecranon. Ossification begins near the middle of the body, 
about the eighth week of fetal life, and soon extends through the greater part of the bone. At birth 
the ends are cartilaginous. About the fourth year, a center appears in the middle of the head, 
and soon extends into the styloid process. About the tenth year, a center appears in the olecranon 
near its extremity, the chief part of this process being formed by an upward extension of the body. 
The upper epiphysis joins the body about the sixteenth, the lower about the twentieth year. 

Articulations. — The ulna articulates with the humerus and radius. 

The Radius. 

The radius (Figs. 213, 214) is situated on the lateral side of the ulna, which 
exceeds it in length and size. Its upper end is small, and forms only a small part 
of the elbow-joint ; but its lower end is large, and forms the chief part of the wrist- 
joint. It is a long bone, prismatic in form and slightly curved longitudinally. It 
has a body and two extremities. 

The Upper Extremity (proximal extremity). — The upper extremity presents a 
head, neck, and tuberosity. The head is of a cylindrical form, and on its upper 
surface is a shallow cup or fovea for articulation with the capitulum of the humerus. 
The circumference of the head is smooth; it is broad medially where it articulates 
with the radial notch of the ulna, narrow in the rest of its extent, which is embraced 
by the annular ligament. The head is supported on a round, smooth, and con- 
stricted portion called the neck, on the back of which is a slight ridge for the inser- 
tion of part of the Supinator. Beneath the neck, on the medial side, is an eminence, 
the radial tuberosity; its surface is divided into a posterior, rough portion, for the 
insertion of the tendon of the Biceps brachii, and an anterior, smooth portion, on 
which a bursa is interposed between the tendon and the bone. 

The Body or Shaft (corpus radii). — The body is prismoid in form, narrower 
above than below, and slightly curved, so as to be convex lateralward. It presents 
three borders and three surfaces. 

Borders. — The volar border (mar go volaris; anterior border) extends from the lower 
part of the tuberosity above to the anterior part of the base of the styloid process 
below, and separates the volar from the lateral surface. Its upper third is promi- 
nent, and from its oblique direction has received the name of the oblique line of the 
radius ; it gives origin to the Flexor digitorum sublimis and Flexor poUicis longus ; the 
surface above the line gives insertion to part of the Supinator. The middle third of 
the volar border is indistinct and rounded. The lower fourth is prominent, and gives 
insertion to the Pronator quadratus, and attachment to the dorsal carpal ligament; 
it ends in a small tubercle, into which the tendon of the Brachioradialis is inserted. 

The dorsal border (margo dorsalis; posterior border) begins above at the back of 
the neck, and ends below at the posterior part of the base of the styloid process; 
it separates the posterior from the lateral surface. It is indistinct above and below, 
but well-marked in the middle third of the bone. 

The interosseous crest (crista interossea; internal or interosseous border) begins 
above, at the back part of the tuberosity, and its upper part is rounded and indis- 
tinct; it becomes sharp and prominent as it descends, and at its lower part divides 
into two ridges which are continued to the anterior and posterior margins of the 
ulnar notch. To the posterior of the two ridges the lower part of the interosseous 



220 OSTEOLOGY 

membrane is attached, while the triangular surface between the ridges gives inser- 
tion to part of the Pronator quadratus. This crest separates the volar from the 
dorsal surface, and gives attachment to the interosseous membrane. 

Surface.^ — The volar surface (fades volaris; anterior surface) is concave in its 
upper three-fourths, and gives origin to the Flexor pollicis longus; it is broad and fiat 
in its lower fourth, and affords insertion to the Pronator quadratus. A prominent 
ridge limits the insertion of the Pronator quadratus below, and between this and 
the inferior border is a triangular rough surface for the attachment of the volar 
radiocarpal ligament. At the junction of the upper and middle thirds of the 
volar surface is the nutrient foramen, which is directed obliquely upward. 

The dorsal surface {fades dorsalis; posterior surface) is convex, and smooth in 
the upper third of its extent, and covered by the Supinator. Its middle third is 
broad, slightly concave, and gives origin to the Abductor pollicis longus above, 
and the Extensor pollicis brevis below. Its lower third is broad, convex, and 
covered by the tendons of the muscles which subsequently run in the grooves on 
the lower end of the bone. 

The lateral surface {fades lateralis; external surface) is convex throughout its 
entire extent. Its upper third gives insertion to the Supinator. About its center is 
a rough ridge, for the insertion of the Pronator teres. Its lower part is narrow, and 
covered by the tendons of the Abductor pollicis longus and Extensor pollicis brevis. 

The Lower Extremity. — The lower extremity is large, of quadrilateral form, 
and provided with two articular surfaces — one below, for the carpus, and another 
at the medial side, for the ulna. The carpal articular surface is triangular, concave, 
smooth, and divided by a slight antero-posterior ridge into two parts. Of these, 
the lateral, triangular, articulates with the navicular bone; the medial, quadri- 
lateral, with the lunate bone. The articular surface for the ulna is called the ulnar 
notch {sigmoid cavity) of the radius; it is narrow, concave, smooth, and articulates 
with the head of the ulna. These two articular surfaces are separated by a promi- 
nent ridge, to which the base of the triangular articular disk is attached; this disk 
separates the wrist-joint from the distal radioulnar articulation. This end of the 
bone has three non-articular surfaces — volar, dorsal, and lateral. The volar surface, 
rough and irregular, affords attachment to the volar radiocarpal ligament. The 
dorsal surface is convex, affords attachment to the dorsal radiocarpal ligament, 
and is marked by three grooves. Enumerated from the lateral side, the first 
groove is broad, but shallow, and subdivided into two by a slight ridge; the lateral 
of these two transmits the tendon of the Extensor carpi radialis longus, the medial 
the tendon of the Extensor carpi radialis brevis. The second is deep but 'narrow, 
and bounded laterally by a sharply defined ridge; it is directed obliquely from above 
downward and lateralward, and transmits the tendon of the Extensor pollicis 
longus. The third is broad, for the passage of the tendons of the Extensor indicis 
proprius and Extensor digitorum communis. The lateral surface is prolonged 
obliquely downward into a strong, conical projection, the styloid process, which 
gives attachment by its base to the tendon of the Brachioradialis, and by its apex 
to the radial collateral ligament of the wrist-joint. The lateral surface of this 
process is marked by a flat groove, for the tendons of the Abductor pollicis longus 
and Extensor pollicis brevis. 

Structure. — The long narrow medullary cavity is enclosed in a strong wall of compact tissue 
which is thickest along the interosseous border and thinnest at the extremities except over the 
cup-shaped articular surface (fovea) of the head where it is thickened. The trabeculae of the 
spongy tissue are somewhat arched at the upper end and pass upward from the compact layer of 
the shaft to the fovea capituli; they are crossed by others parallel to the surface of the fovea. 
The arrangement at the lower end is somewhat similar. 

Ossification (Figs. 217, 218). — The radius is ossified from three centers: one for the body, 
and one for either extremity. That for the body makes its appearance near the center of the bone, 
during the eighth week of fetal hfe. About the end of the second year, ossification commences 



THE CARPUS 



221 



in the lower end; and at the fifth year, in the upper end. The upper epiphysis fuses with the 
body at the age of seventeen or eighteen years, the lower about the age of twenty. An additional 
center sometimes found in the radial tuberosity, appears about the fourteenth or fifteenth year. 



Appears ai_ 
fifth year 



Bend 
■fa^ \ Unites with body 



about pvherty 



u 

Body 



I 

Appears "'^'C*^^^ T\ Unites with body 
second year I ^^^^^ ai)out twentieth 

year 
Lower extremity 



Fig. 217. — -Plan of ossification of the radius. 
From three centers. 





Fig. 218. — Epiphysial lines of radius in a young 
adult. Anterior aspect. The line of attachment of the 
articular capsule of the wrist-joint is in blue. 



THE HAND. 

The skeleton of the hand (Fijjs. 219, 220) is subdivided into three segments: the 
carpus or wrist bones; the metacarpus or bones of the palm; and the phalanges or 
bones of the digits. 

The Carpus (Ossa Carpi). 

The carpal bones, eight in number, are arranged in two rows. Those of the 
proximal row, from the radial to the ulnar side, are named the navicular, limate, 
triangular, and pisiform; those of the distal row, in the same order, are named the 
greater multangular, lesser multangular, capitate, and hamate. 

Common Characteristics of the Carpal Bones. — Each bone (excepting the pisi- 
form) presents six surfaces. Of these the volar or anterior and the dorsal or jmsterior 
surfaces are. rough, for ligamentous attachment; the dorsal surfaces being the 
broader, except in the navicular and lunate. The superior or yroximal, and inferior 
or distal surfaces are articular, the superior generally convex, the inferior concave; 
the medial and lateral surfaces are also articular where they are in contact with 
contiguous bones, otherwise they are rough and tuberculated. The structure :n 
all is similar, viz., cancellous tissue enclosed in a layer of compact bone. 

Bones of the Proximal Row (upper row). — The Navicular Bone (os naviculare manus; 
scaphoid hone) (Fig. 221).^ — The navicular bone is the largest bone of the proximal 
row, and has received its name from its fancied resemblance to a boat. It is situated 
at the radial side of the carpus, its long axis being from above downward, lateralward, 
and forward. The superior surface is convex, smooth, of triangular shape, and artic- 



222 



OSTEOLOGY 



ulates with the lower end of the radius. The inferior surface, directed downward, 
lateralward, and backward, is also smooth, convex, and triangular, and is divided 
by a slight ridge into two parts, the lateral articulating with the greater multangu- 
lar, the medial with the lesser multangular. On the dorsal surface is a narrow, 
rough groove, which runs the entire length of the bone, and serves for the attach- 
ment of ligaments. The volar surface is concave above, and elevated at its lower 
and lateral part into a rounded projection, the tubercle, which is directed forward 



Carfiis 

Flexor carpi ulnakis 

Flexor digiti quinti brevis 
Opponess digiti quinti 



Groove for tendon of 
Flexor carpi radialis 

Opposexs pollicis 
Flexor pollicis brevis 



y Abductor pollicis 

■ LONGDs 



Metacarpus 



Plexor brevis "\ 
axd I 

Abductor f 
digiti quisti. ) 




Sesamoid 
bones 



Abductor 
pollicis 
brevis 



FU:X0R DIGITORUM SUBLIMIS 



Flexor digitoruii profundus 



Fig. 219. — Bones of the left hand. Volar surface. 



THE CARPUS 



223 



and gives attachment to the transverse carpal Hgament and sometimes origin to 
a few fibers of the Abductor pollicis brevis. The lateral surface is rough and narrow, 
and gives attachment to the radial collateral ligament of the wrist. The medial 
siirface presents two articular facets; of these, the superior or smaller is flattened 
of semilunar form, and articulates with the lunate bone; the inferior or larger is 
concave, forming with the lunate a concavity for the head of the capitate bone. 



^<*^^iM;^^ 



\r- Carptia 



Ext. carpi rapialis 

LOSGCS 



Ext. carpi radialis 

BREVIS "7^ 



Ext. carpi itlnaris 



Metacarpus 



Ext. 

POLLICI? 
10NGC3 




TTialanges 
i'^ Bow 



Z^rttm 



Ext. diqitorum 
coMMrNis and 
Ext. indicis 

PROPRirS. 



i'^Rove 



FiQ. 220. — Bones of the left hand. Dorsal surface. 



224 



OSTEOLOGY 



Articulations. — The navicular articulates with five bones: the radius proximally, greater and 
lesser multangulars distally, and capitate and lunate medially. 

The Lunate Bone {os lunatum; semilunar bone) (Fig. 222). — The lunate bone may 
be distinguished by its deep concavity and crescentic outHne. It is situated in 
the center of the proximal row of the carpus, between the navicular and triangular. 
The superior surface, convex and smooth, articulates with the radius. The inferior 
surface is deeply concave, and of greater extent from before backward than trans- 



For radius 



For lunate 



Tubercle 



For greater 
multangular 





For capitate 



For lesser multangular 
Fig. 221. — The left navicular bone. 



versely: it articulates with the head of the capitate, and, by a long, narrow facet 
(separated by a ridge from the general surface), with the hamate. The dorsal 
and volar surfaces are rough, for the attachment of ligaments, the former being 
the broader, and of a somewhat rounded form. The lateral surface presents a 



For triangular 



For radius 





For navicular 
For Iiamate For capitate 

FiQ. 222.— The left lunate bone. 

narrow, flattened, semilunar facet for articulation with the navicular. The medial 
surface is marked by a smooth, quadrilateral facet, for articulation with the 
triangular. 

Articulations. — The lunate articulates witli five bones: the radius proximally, capitate and 
hamate distally, navicular laterally, and triangular medially. 



Fof pisiform 



For lunate 




For triangular 




Fig. 224. — The left pisiform bone. 



For hamate 
Fig. 223.— The left triangular bone. 

The Triangular Bone (os triquetum; cuneiform hone) (Fig. 223).- — The triangular 
bone may be distinguished by its pyramidal shape, and by an oval isolated facet 
for articulation with the pisiform bone. It is situated at the upper and ulnar side 
of the carpus. The superior surface presents a medial, rough, non-articular portion, 
and a lateral convex articular portion which articulates with the triangular articular 
disk of the wrist. The inferior surface, directed lateralward, is concave, sinuously 
curved, and smooth for articulation with the hamate. The dorsal surface is rough 
for the attachment of ligaments. The volar surface presents, on its medial part, 



THE CARPUS 



225 



an oval facet, for articulation with the pisiform; its lateral part is rough for liga- 
mentous attachment. The lateral surface, the base of the pyramid, is marked by a 
flat, quadrilateral facet, for articulation with the lunatel The medial surface, 
the summit of the pyramid, is pointed and roughened, for the attachment of the 
ulnar collateral ligament of the wrist. 

Articulations.— The triangular articulates with three bones: the lunate laterally, the pisiform 
in front, the hamate distally; and with the triangular articular disk which separates it from the 
lower end of the ulna. 

The Pisiform Bone {os pisiforme) (Fig. 224).— The pisiform bone may be known 
by its small size, and by its presenting a single articular facet. It is situated on a 
plane anterior to the other carpal bones and is spheroidal in form. Its dorsal 
surface presents a smooth, oval facet, for articulation with the triangular: this facet 
approaches the superior, but not the inferior border of the bone. The volar surface 
is rounded and rough, and gives attachment to the transverse carpal ligament, 
and to the Flexor carpi ulnaris and Abductor digiti quinti. The lateral and medial 
surfaces are also rough, the former being concave, the latter usually convex. 

Articulation. — The pisiform articulates with one bone, the triangular. 

Bones of the Distal Row [lower row). — The Greater Multangular Bone {os mul-' 
tangulum majus; trapezium) (Fig. 225).— The greater multangular bone may be 
distinguished by a deep groove on its volar surface. It is situated at the radial 
side of the carpus, between the navicular and the first metacarpal bone. The 
superior surface is directed upward and medialward; medially it is smooth, and 
articulates with the navicular; laterally it is rough and continuous with the lateral 
surface. The inferior surface is oval, concave from side to side, convex from before 
backward, so as to form a saddle-shaped surface for articulation with the base 



For lesser 
multangular 



Groove 



For 2nd 
metacarpal 




For navicular 



Ridge 



For \st metacarpal 

Fig. 225. — The left greater multangular bone 




For lesser 
multangular 



For 2iui metacarpal 



of the first metacarpal bone. The dorsal surface is rough. The volar surface is 
narrow and rough. At its upper part is a deep groove, running from above obliquely 
downward and medialward; it transmits the tendon of the Flexor carpi radialis, 
and is bounded laterally by an oblique ridge. This surface gives origin to the 
Opponens pollicis and to the Abductor and Flexor pollicis brevis; it also affords 
attachment to the transverse carpal ligament. The lateral surface is broad and 
rough, for the attachment of ligaments. The medial surface presents two facets; 
the upper, large and concave, articulates with the lesser multangular; the lower, 
small and oval, with the base of the second metacarpal. 

Articulations. — -The greater multangular articulates with four bones : the navicular proximally, 
the first metacarpal distally, and the lesser multangular and second metacarpal medially. 

The Lesser Multangular Bone {os multangulum minus; trapezoid bone) (Fig. 226). 
— The lesser multangular is the smallest bone in the distal row. It may be known 
by its wedge-shaped form, the broad end of the wedge constituting the dorsal, 
the narrow end the volar surface; and by its having four articular facets touching 
each other, and separated by sharp edges. The superior surface, quadrilateral, 
15 



226 



OSTEOLOGY 



For navicular 



Volar 
surface 



For greater 
multan/fular 



smooth, and slightly concave, articulates with the navicular. The inferior surface 
articulates with the proximal end of the second metacarpal bone; it is convex from 
side to side, concave from before backward and subdivided by an elevated ridge into 

two unequal facets. The dorsal and volar 
surfaces are rough for the attachment of 
ligaments, the former being the larger 
of the two. The lateral surface, convex 
and smooth, articulates with the greater 
multangular. The medial surface is con- 
cave and smooth in front, for artic- 
ulation with the capitate; rough behind, 
for the attachment of an interosseous 





Dorsal For 

surface capitate 

Fig. 226. — The left lesser multangular bone 



For 2ndr 
metacarpal 



ligament. 



Articulations. — The lesser multangular articulates with four bones : the navicular proximally, 
second metacarpal distally, greater multangular laterally; and capitate medially. 

The Capitate Bone {os capitatum; os magnum) (Fig. 227). — The capitate bone 
is the largest of the carpal bones, and occupies the center of the wrist. It presents, 
above, a rounded portion or head, which is received into the concavity formed by 



For lunate 



Far 
navicular 



For lesser 
multangular 




For 
hamate '-j^ 



For 3rd 
For 2nd metacarpal 
metacarpal 




For 4:th metacarpal Volar surface 

Fig. 227. — The left capitate bone. 



the navicular and lunate; a constricted portion or neck; and below this, the body. 
The superior surface is round, smooth, and articulates with the lunate. The inferior 
surface is divided by two ridges into three facets, for articulation with the second, 
third, and fourth metacarpal bones, that for the third being the largest. The 
dorsal surface is broad and rough. The volar surface is narrow, rounded, and rough, 
for the attachment of ligaments and a part of the Adductor pollicis obliquus. 



For lunai& 




For capitate 



For triangular 



For 4th metacarpal 



For 5th metacarpal Hamulus 

Fig. 228. — The left hamate bone. 




For 5th metacarpal 



The lateral surface articulates with the lesser multangular by a small facet at 
its anterior inferior angle, behind which is a rough depression for the attach- 
ment of an interosseous ligament. Above this is a deep, rough groove, forming 
part of the neck, and serving for the attachment of ligaments; it is bounded supe- 
riorly by a smooth, convex surface, for articulation with the navicular. The medial 



THE METACARPUS 227 

surface articulates with the hamate by a smooth, concave, oblong facet, which 
occupies its posterior and superior parts; it is rough in front, for the attachment 
of an interosseous ligament. 

Articulations. — The capitate articulates with seven bones: the navicular and lunate proximally, 
the second, third, and fourth metacarpals distally, the lesser multangular on the radial side, and 
the hamate on the ulnar side. 

The Hamate Bone {os hamaium; unciform bone) (Fig. 228). — The hamate bone 
may be readily distinguished by its wedge-shaped form, and the hook-like process 
which projects from its volar surface. It is situated at the medial and lower angle 
of the carpus, with its base downward, resting on the fourth and fifth metacarpal 
bones, and its apex directed upward and lateralward. The superior surface, the 
apex of the wedge, is narrow, convex, smooth, and articulates with the lunate. 
The inferior surface articulates with the fourth and fifth metacarpal bones, by 
concave facets which are separated by a ridge. The dorsal surface is triangular 
and rough for ligamentous attachment. The volar surface presents, at its lower 
and ulnar side, a curved, hook-like process, the hamulus, directed forward and 
lateralward. This process gives attacliment, by its apex, to the transverse carpal 
ligament and the Flexor carpi ulnaris; by its medial surface to the Flexor brevis 
and Opponens digiti quinti; its lateral side is grooved for the passage of the Flexor 
tendons into the palm of the hand. It is one of the four eminences on the front 
of the carpus to which the transverse carpal ligament of the wrist is attached; 
the others being the pisiform medially, the oblique ridge of the greater multangular 
and the tubercle of the navicular laterally. The medial surface articulates with 
the triangular bone by an oblong facet, cut obliquely from above, downward 
and medialward. The lateral surface articulates with the capitate by its upper 
and posterior part, the remaining portion being rough, for the attachment of 
ligaments. 

Articulations. — The hamate articulates with five bones: the lunate proximally, the fourth 
and fifth metacarpals distally, the triangular medially, the capitate laterally. 

The Metacarpus. 

The metacarpus consists of five cylindrical bones which are numbered from the 
lateral side {ossa metacarpalia I-V); each consists of a body and two extremities. 

Common Characteristics of the Metacarpal Bones. — The Body (corpus; shaft). — 
The body is prismoid in form, and curved, so as to be convex in the longitudinal 
direction behind, concave in front. It presents three surfaces: medial, lateral, 
and dorsal. The medial and lateral surfaces are concave, for the attachment of 
the Interossei, and separated from one another by a prominent anterior ridge. 
The dorsal siu-face presents in its distal two-thirds a smooth, triangular, flattened 
area which is covered in the fresh state, by the tendons of the Extensor muscles. 
This surface is bounded bv two lines, which commence in small tubercles situated 
on either side of the digital extremity, and, passing upward, converge and meet 
some distance above the center of the bone and form a ridge which runs along the 
rest of the dorsal surface to the carpal extremity. This ridge separates two 
sloping surfaces for the attachment of the Interossei dorsales. To the tubercles 
on the digital extremities are attached the collateral ligaments of the metacarpo- 
phalangeal joints. 

The Base or Carpal Extremity (baMs) is of a cuboidal form, and broader behind 
than in front: it articulates with the carpus, and with the adjoining metacarpal 
bones; its dorsal and volar surfaces are rough, for the attachment of ligaments. 

The Head or Digital Extremity (capitulwn) presents an oblong surface markedly 
convex from before backward, less so transversely, and flattened from side to side; 
it articulates with the proximal phalanx. It is broader, and extends farther up- 



228 



OSTEOLOGY 





For greater 
mvltangular 



For greater 
mxdtangvlar 



Fig. 229. — The first metacarpal. 
(Left.) 



ward, on the volar than on the dorsal aspect, and is longer in the antero-posterior 
than in the transverse diameter. On either side of the head is a tubercle for the 
attachment of the collateral ligament of the metacarpophalangeal joint. The 
dorsal surface, broad and flat, supports the Extensor tendons; the volar surface 
is grooved in the middle line for the passage of the Flexor tendons, and marked 
on either side by an articular eminence continuous with the terminal articular 
surface. 

Characteristics of the Individual Metacarpal Bones. — The First Metacarpal 
Bone ips metacarpale I; metacarpal bone of the thumb) (Fig. 229) is shorter and 

stouter than the others, diverges to a greater degree 
from the carpus, and its A'olar surface is directed 
toward the palm. The body is flattened and broad 
on its dorsal surface, and does not present the ridge 
which is found on the other metacarpal bones; its 
volar surface is concave from above downward. On 
its radial border is inserted the Opponens pollicis; 
its ulnar border gives origin to the lateral head of 
the first Interosseus dorsalis. The base presents a 
concavo-convex surface, for articulation with the 
greater multangular; it has no facets on its sides, but 
on its radial side is a tubercle for the insertion of the 
Abductor pollicis longus. The head is less convex 
than those of the other metacarpal bones, and is 
broader from side to side than from before backward. 
On its volar surface are two articular eminences, of 
which the lateral is the larger, for the two sesamoid 
bones in the tendons of the Flexor pollicis brevis. 
The Second Metacarpal Bone {os metacarpale II; metacarpal bone of the index 
finger) (Fig. 230) is the longest, and its base the largest, of the four remaining 
bones. Its base is prolonged upward and medialward, forming a prominent ridge. 
It presents four articular facets: three on the upper surface and one on the ulnar 
side. Of the facets on the upper surface the intermediate is the largest and is 
concave from side to side, convex from before backward for articulation with the 
lesser multangular ; the lateral is small, flat and oval for articulation with the greater 
multangular; the medial, on the summit of the ridge, is long and narrow for articu- 
lation with the capitate. The facet on the ulnar side articulates with the third 
metacarpal. The Extensor carpi radialis longus is inserted on the dorsal surface 
and the Flexor carpi radialis on the volar surface of the base. 

The Third Metacarpal Bone {os metacarpale III; metacarpal bone of the middle 
finger) (Fig. 231) is a little smaller than the second. The dorsal aspect of its 
base presents on its radial side a pyramidal eminence, the styloid process, which 
extends upward behind the capitate; immediately distal to this is a rough surface 
for the attachment of the Extensor carpi radialis brevis. The carpal articular 
facet is concave behind, flat in front, and articulates with the capitate. On the 
radial side is a smooth, concave facet for articulation with the second metacarpal, 
and on the ulnar side two small oval facets for the fourth metacarpal. 

The Fourth Metacarpal Bone {os metacarpale IV; metacarpal bone of the ring 
finger) (Fig. 232) is shorter and smaller than the third. The base is small and 
quadrilateral; its superior surface presents two facets, a large one medially for 
articulation with the hamate, and a small one laterally for the capitate. On the 
radial side are two oval facets, for articulation with the third metacarpal ; and on 
the ulnar side a single concave facet, for the fifth metacarpal. 

The Fifth Metacarpal Bone {os metacarpale V; metacarpal bone of the little finger) 
(Fig. 233) presents on its base one facet on its superior surface, which is concavo- 



THE METACARPUS 



229 



convex and articulates with the hamate, and one on its radial side, which articuhates 
with the fourth metacarpal. On its ulnar side is a prominent tubercle for the inser- 
tion of the tendon of the Extensor carpi ulnaris. The dorsal surface of the body 




For greater 
For le.iser multangular 
multangular 




For 6rd 

metacarpal For For lesser 
capitate mult- 
angular 




Fio. 230. — The second metacarpal. (Left.) 



Styloid For 2nd For For ^ih 

process meta- capitate metacarpal 

carpal 

Fig. 231. — The third metacarpal. (Left.) 



is divided by an oblique ridge, which extends from near the ulnar side of the base 
to the radial side of the head. The lateral part of this surface serves for the attach- 
ment of the fourth Interosseus dorsalis; the medial part is smooth, triangular, and 
covered by the Extensor tendons of the little finger. 





For ^ / ^'or 5th 

capitate ^("' '^''^ ^or meta- 

metacarjMl hamate carpal 

Fig. 232. — The fourth metacarpal. (Left.) 



For 4th 
metacarpal 




For hamate 



Fig. 233. — The fifth metacarpal. (Left.) 



Articulations. — Besides their phalangeal articulations, the metacarpal bones articulate as 
follows: the first with the greater multangular; the second with the greater multangular, lesser 
multangular, capitate and third metacarpal; the third with the capitate and second and fourth 
metacarpals; the fourth with the capitate, hamate, and third and fifth metacarpals; and the 
fifth with the hamate and fourth metacarpal. 



230 



OSTEOLOGY 



The Phalanges of the Hand (Phalanges Digitorum Manus). 

The phalanges are fourteen in number, three for each finger, and two for the 
thumb. Each consists of a body and two extremities. The body tapers from above 
downward, is convex posteriorly, concave in front from above downward, fiat 
from side to side; its sides are marked by rough ridges which give attachment 
to the fibrous sheaths of the Flexor tendons. The proximal extremities of the bones 
of the first row present oval, concave articular surfaces, broader from side to side 
than from before backward. The proximal extremity of each of the bones of the 
second and third rows presents a double concavity separated by a median ridge. 
The distal extremities are smaller than the proximal, and each ends in two condyles 
separated by a shallow groove; the articular surface extends farther on the volar 
than on the dorsal surface, a condition best marked in the bones of the first row. 

The ungual phalanges are convex on their dorsal and flat on their volar surfaces; 
they are recognized by their small size, and by a roughened, elevated surface of 
a horseshoe form on the volar surface of the distal extremity of each which serves 
to support the sensitive pulp of the finger. 



CARPUS 

One center for each bone : 
All curlilaginous at birth 






METACARI'ALS OF FINGERS 

Tivo centers for each bone . 
One for body 
One for head 



PHALANGES 



Two centers for each bone 
One for body 
One for proximal 
extremity 




^~.p-\ tini/f 18 20'ty^ 

lip I Sl*;vk 




Off 



S'.'iujS 



Js 



Pia. 234. — Plan of ossification of the hand. 



Articulations. — In the four fingers the phalanges of the first row articulate with those of the 
second row and with the metacarpals; the phalanges of the second row with those of the first 
and third rows, and the ungual phalanges with those of the second row. In the thumb, which 
has only two phalanges, the first phalanx articulates by its proximal extremity with the meta- 
carpal bone and by its distal with the ungual phalanx. 

Ossification of the Bones of the Hand.- — The carpal bones are each ossified from a single center, 
and ossification proceeds in the following order (Fig. 2 34): in the capitate and hamate, during 



THE HIP BONE 231 

the first year, the former preceding the latter; in the triangular, during the third year; in the 
lunate and greater multangular, during the fifth year, the former preceding the latter; in the 
navicular, during the sixth year; in the lesser multangular, during the eighth year; and in 
the pisiform, about the twelfth year 

Occasionally an additional bone, the os centrale, is found on the back of the carpus, lying 
between the navicular, lesser multangular, and capitate. During the second month of fetal hfe 
it is represented by a small cartilaginous nodule, which usually fuses with the cartilaginous navic- 
ular. Sometimes the styloid process of the third metacarpal is detached and forms an additional 
ossicle. 

The metacarpal bones are each ossified from two centers: one for the body and one for the 
distal extremity of each of the second, third, fourth, and fifth bones; one for the body and one 
for the base of the first metacarpal bone.^ The first metacarpal bone is therefore ossified in the 
same manner as the phalanges, and this has led some anatomists to regard the thumb as being 
made up of three phalanges, and not of a metacarpal bone and two phalanges. Osssification com- 
mences in the middle of the body about the eighth or ninth week of fetal hfe, the centers for the 
second and third metacarpals being the first, and that for the first metacarpal, the last, to appear; 
about the third year the distal extremities of the metacarpals of the fingers, and the base of the 
metacarpal of the thumb, begin to ossify; they unite with the bodies about the twentieth year. 

The phalanges are each ossified from two centers: one for the body, and one for the proximal 
extremity. Ossification begins in the body, about the eighth week of fetal life. Ossification of 
the proximal extremity commences in the bones of the first row between the third and fourth 
years, and a year later in those of the second and third rows. The two centers become united 
in each row between the eighteenth and twentieth years. 

In the ungual phalanges the centers for the bodies appear at the distal extremities of the 
phalanges, instead of at the middle of the bodies, as in the other phalanges. Moreover, of all 
the bones of the hand, the ungual phalanges are the first to ossify. 

THE BONES OF THE LOWER EXTREMITY (OSSA EXTREMITATIS INFERIORIS). 

The Hip Bone (Os Coxse; Innominate Bone). 

The hip bone is a large, flattened, irregularly shaped bone, constricted in the 
center and expanded above and below. It meets its fellow on the opposite side 
in the middle line in front, and together they form the sides and anterior wall of 
the pelvic cavity. It consists of three parts, the ilium, ischium, and pubis, which 
are distinct from each other in the young subject, but are fused in the adult; 
the union of the three parts takes place in and around a large cup-shaped articular 
cavity, the acetabulum, which is situated near the middle of the outer surface of the 
bone. The ilium, so-called because it supports the flank, is the superior broad and 
expanded portion which extends upward from the acetabulum. The ischium is the 
lowest and strongest portion of the bone; it proceeds downward from the acetab- 
ulum, expands into a large tuberosity, and then, curving forward, forms, with 
the pubis, a large aperture, the obturator foramen. The pubis extends medialward 
and downward from the acetabulum and articulates in the middle line with the 
bone of the opposite side : it forms the front of the pelvis and supports the external 
organs of generation. 

The lUum (os ilii). — The ilium is divisible into two parts, the body and the 
ala ; the separation is indicated on the internal surface by a curved line, the arcuate 
line, and on the external surface by the margin of the acetabulum. 

The Body {corpus oss. ilii). — The body enters into the formation of the acetab- 
ulum, of which it forms rather less than two-fifths. Its external surface is partly 
articular, partly non-articular; the articular segment forms part of the lunate 
surface of the acetabulum, the non-articular portion contributes to the acetabular 
fossa. The internal surface of the body is part of the wall of the lesser pelvis and 
gives origin to some fibers of the Obturator internus. Below, it is continuous with 
the pelvic surfaces of the ischium and pubis, only a faint line indicating the place 
of union. 

' Allen Thomson demonstrated the fact that the first metacarpal bone is often developed from three o_enters: that is 
to say, there is a separate nucleus for the distal end, forming a distinct epiphysis visible at the age of seven or eight 
years. He also stated that there are traces of a proximal epiphysis in the second metacarpal bone. Journal of Anatomy 
and Physiology, 1869. 



232 



OSTEOLOGY 



The Ala {ala oss. ilii). — The ala is the large expanded portion which bounds 
the greater pelvis laterally. It presents for examination two surfaces — ^an external 
and an internal — a crest, and two borders- — an anterior and a posterior. The 
external surface (Fig. 235), known as the dorsum ilii, is directed backward and lateral- 
ward behind, and downward and lateralward in front. It is smooth, convex in front, 



Ant. superior 
spine 



Posterior 

superior 

spine 




— Anterior inferior spine 



Posterior 
inferior 
spine 



Articular capsule 
Ligament um teres 



Gemellus superior 
Spine of ischium— 

Gemellus inferior 



Rectus 
abdominis 



Pyramidalis 



Adductor 
longus 



Fig. 235. — Right hip bone. External surface. 



deeply concave behind; bounded above by the crest, below by the upper border 
of the acetabulum, in front and behind by the anterior and posterior borders. 
This surface is crossed in an arched direction by three lines — the posterior, anterior, 
and inferior gluteal lines. The posterior gluteal line (superior curved line), the short- 
est of the three, begins at the crest, about 5 cm. in front of its posterior ex-tremity; 
it is at first distinctly marked, but as it passes downward to the upper part of the 



THE HIP BONE 



233 



greater sciatic notch, where it ends, it becomes less distinct, and is often altogether 
lost. Behind this line is a narrow semilunar surface, the upper part of which 
is rough and gives origin to a portion of the Gluteus maximus; the lower part is 
smooth and has no muscular fibers attached to it. The anterior gluteal Une (middle 
curved line), the longest of the three, begins at the crest, about 4 cm. behind its 
anterior extremity, and, taking a curved direction downward and backward, ends 




Levator ani 



Constrictor vrethroe 

Transversus perinoei superfic, 

Crus penis Ischiocavernosus 
FiQ. 236. — Right hip bone. Internal surface. 



at the upper part of the greater sciatic notch. The space between the anterior 
and posterior gluteal lines and the crest is concave, and gives origin to the Glutseus 
medius. Xear the middle of this line a nutrient foramen is often seen. The 
inferior gluteal line {inferior curved line), the least distinct of the three, begins in 
front at the notch on the anterior border, and, curving backward and downward, 
ends near the middle of the greater sciatic notch. The surface of bone included 



234 OSTEOLOGY 

between the anterior and inferior gluteal lines is concave from above downward, 
convex from before backward, and gives origin to the Glutfeus minimus. Between 
the inferior gluteal line and the upper part of the acetabulum is a rough, shallow 
g^oo^•e, from which the reflected tendon of the Rectus femoris arises. 

The internal surface (Fig. 236) of the ala is bounded above by the crest, below, 
by the arcuate line; in front and behind, by the anterior and posterior borders. 
It presents a large, smooth, concave surface, called the iliac fossa, which gives 
origin to the Iliacus and is perforated at its inner part by a nutrient canal; and 
below this a smooth, rounded border, the arcuate line, which runs downward, for- 
ward, and medialward. Behind the iliac fossa is a rough surface, divided into two 
portions, an anterior and a posterior. The anterior surface (auricular surface), 
so called from its resemblance in shape to the ear, is coated with cartilage in the 
fresh state, and articulates with a similar surface on the side of the sacrum. 
The posterior portion, known as the iliac tuberosity, is elevated and rough, for 
the attachment of the posterior sacroiliac ligaments and for the origins of the 
Sacrospinalis and ]Multifidus. Below and in front of the auricular surface is the 
preauricular sulcus, more commonly present and better marked in the female 
than in the male; to it is attached the pelvic portion of the anterior sacroiliac 
ligament. 

The crest of the ilium is convex in its general outline but is sinuously curved, 
being concave inward in front, concave outward behind. It is thinner at the center 
than at the extremities, and ends in the anterior and posterior superior iliac spines. 
The surface of the crest is broad, and divided into external and internal lips, 
and an intermediate line. About 5 cm. behind the anterior superior iliac spine 
there is a prominent tubercle on the outer lip. To the external lip are attached 
the Tensor' fasciae latse, Obliquus externus abdominis, and Latissimus dorsi, and 
along its whole length the fascia lata ; to the intermediate line the Obliquus internus 
abdominis; to the internal lip, the fascia iliaca, the Transversus abdominis, 
Quadratus lumborum, Sacrospinalis, and Iliacus. 

The anterior border of the ala is concave. It presents two projections, separated 
by a notch. Of these, the uppermost, situated at the junction of the crest and 
anterior border, is called the anterior superior iliac spine; its outer border gives 
attachment to the fascia lata, and the Tensor fasciie lattv, its inner border, to the 
Iliacus; while its extremity affords attachment to the inguinal ligament and gives 
origin to the Sartorius. Beneath this eminence is a notch from which the Sartorius 
takes origin and across which the lateral femoral cutaneous nerve passes. Below 
the notch is the anterior inferior iliac spine, which ends in the upper lip of the 
acetabulum; it gives attachment to the straight tendon of the Rectus femoris and 
to the iliofemoral ligament of the hip-joint. Medial to the anterior inferior spine 
is a broad, shallow groove, over which the Iliacus and Psoas major pass. This 
groove is boimded medially by an eminence, the iliopectineal eminence, which 
marks the point of union of the ilium and pubis. 

The posterior border of the ala, shorter than the anterior, also presents two 
projections separated by a notch, the posterior superior iliac spine and the posterior 
inferior iliac spine. The former serves for the attachment of the oblique portion 
of the posterior sacroiliac ligaments and the Multifidus; the latter corresponds 
with the posterior extremity of the auricular surface. Below the posterior inferior 
spine is a deep notch, the greater sciatic notch. 

The Ischium (os ischii). — The ischium forms the lower and back part of the 
hip bone. It is divisible into three portions — a body and two rami. 

The Body (corpus oss. ischii). — The body enters into and constitutes a little 
more than two-fifths of the acetabulum. Its external surface forms part of the 
lunate surface of the acetabulum and a portion of the acetabular fossa. Its internal 
surface is part of the wall of the lesser pelvis; it gives origin to some fibers of the 



THE HIP BONE 235 

Obturator internus. Its anterior border projects as the posterior obturator tubercle; 
from its posterior border there extends backward a thin and pointed triangular 
eminence, the ischial spine, more or less elongated in different subjects. The 
external surface of the spine gives attachment to the Gemellus superior, its internal 
surface to the Coccygeus, Levator ani, and the pelvic fascia; while to the pointed 
extremity the sacrospinous ligament is attached. Above the spine is a large notch, 
the greater sciatic notch, converted into a foramen by the sacrospinous ligament; 
it transmits the Piriformis, the superior and inferior gluteal vessels and nerves, 
the sciatic and posterior femoral cutaneous nerves, the internal pudendal vessels, 
and nerve, and the nerves to the Obturator internus and Quadratus femoris. Of 
these, the superior gluteal vessels and nerve pass out above the Piriformis, the 
other structures below it. Below the spine is a smaller notch, the lesser sciatic 
notch; it is smooth, coated in the recent state with cartilage, the surface of which 
presents two or three ridges corresponding to the subdivisions of the tendon of 
the Obturator internus, which winds over it. It is converted into a foramen by 
the sacrotuberous and sacrospinous ligaments, and transmits the tendon of the 
Obturator internus, the nerve which supplies that muscle, and the internal 
pudendal vessels and nerve. 

The Superior Ramus (ramus superior oss. ischii; descending ramus). — The 
superior ramus projects downward and backward from the body and presents 
for examination three surfaces: external, internal, and posterior. The external 
surface is quadrilateral in shape. It is bounded above by a groove which lodges 
the tendon of the Obturator externus; below, it is continuous with the inferior 
ramus; in front it is limited by the posterior margin of the obturator foramen; 
behind, a prominent margin separates it from the posterior surface. • In front of 
this margin the surface gives origin to the Quadratus femoris, and anterior to this 
to some of the fibers of origin of the Obturator externus; the lower part of the sur- 
face gives origin to part of the Adductor magnus. The internal surface forms part 
of the bony wall of the lesser pelvis. In front it is limited by the posterior margin 
of the obturator foramen. Below, it is bounded by a sharp ridge which gives 
attachment to a falciform prolongation of the sacrotuberous ligament, and, more 
anteriorly, gives origin to the Transversus perina^i and Ischiocavernosus. Poste- 
riorly the ramus forms a large swelling, the tuberosity of the ischium, which is divided 
into two portions: a lower, rough, somewhat triangular part, and an upper, smooth, 
quadrilateral portion. The lower portion is subdivided by a prominent longitudinal 
ridge, passing from base to apex, into two parts; the outer gives attachment to 
the Adductor magnus, the inner to the sacrotuberous ligament. The upper portion 
is subdivided into two areas by an oblique ridge, which runs downward and out- 
ward; fiom the upper and outer area the Semimembranosus arises; from the lower 
and inner, the long head of the Biceps femoris and the Semitendinosus. 

The Inferior Ramus (ramus inferior oss. ischii; ascending ramus).- — The inferior 
ramus is the thin, flattened part of the ischium, which ascends from the superior 
ramus, and joins the inferior ramus of the pubis — the junction being indicated in 
the adult by a raised line. The outer siu:f ace is uneven for the origin of the Obturator 
externus and some of the fibers of the Adductor magnus; its inner surface forms 
part of the anterior wall of the pelvis. Its medial border is thick, rough, slightly 
everted, forms part of the outlet of the pelvis, and presents two ridges and an 
intervening space. The ridges are continuous with similar ones on the inferior 
ramus of the pubis: to the outer is attached the deep layer of the superficial peri- 
neal fascia (fascia of Colles), and to the inner the inferior fascia of the urogenital 
diaphragm. If these two ridges be traced downward, they will be found to join 
with each other just behind the point of origin of the Transversus perina^i; here 
the two layers of fascia are continuous behind the posterior border of the muscle. 
To the intervening space, just in front of the point of junction of the ridges, the 



236 OSTEOLOGY 

Transversus perineal is attached, and in front of this a portion of the cms penis 
vel cHtoridis and the Ischiocavernosus. Its lateral border is thin and sharp, and 
forms part of the medial margin of the obturator foramen. 

The Pubis {os jyubis). — The pubis, the anterior part of the hip bone, is divisible 
into a body, a superior and an inferior ramus. 

The Body {corpus oss. pubis). — The body forms one-fifth of the acetabulum, 
contributing by its external surface both to the lunate surface and the acetabular 
fossa. Its internal surface enters into the formation of the wall of the lesser pelvis 
and gives origin to a portion of the Obturator internus. 

The Superior Ramus (ramus superior oss. pubis; ascending ramus). — The superior 
ramus extends from the body to the median plane where it articulates with its 
fellow of the opposite side. It is conveniently described in two portions, viz., a 
medial flattened part and a narrow lateral prismoid portion. 

The Medial Portion of the superior ramus, formerly described as the body of 
the pubis, is somewhat quadrilateral in shape, and presents for examination two 
surfaces and three borders. The anterior surface is rough, directed downward and 
outward, and serves for the origin of various muscles. The Adductor longus arises 
from the upper and medial angle, unmediately below the crest; lower down, the 
Obturator externus, the Adductor brevis, and the upper part of the Gracilis take 
origin. The posterior surface, convex from above downward, concave from side 
to side, is smooth, and forms part of the anterior wall of the pelvis. It gives origin 
to the Levator ani and Obturator internus, and attachment to the puboprostatic 
ligaments and to a few muscular fibers prolonged from the bladder. The upper 
border presents a prominent tubercle, the pubic tubercle (pubic spine), which pro- 
jects forward; the inferior cms of the subcutaneous inguinal ring (external abdominal 
ring), and the inguinal ligament (Pouparfs ligament) are attached to it. Passing 
upward and lateralward from the pubic tubercle is a well-defined ridge, forming 
a part of the pectineal line which marks the brim of the lesser pelvis: to it are 
attached a portion of the inguinal falx (conjoined tendon of Obliquus internus 
and Transversus), the lacunar ligament (Gimbernafs ligament), and the reflected 
inguinal ligament (triangular fascia). Medial to the pubic tubercle is the crest, 
which extends from this process to the medial end of the bone. It affords attach- 
ment to the inguinal falx, and to the Rectus abdominis and Pyramidalis. The 
point of junction of the crest with the medial border of the bone is called the angle; 
to it, as well as to the symphysis, the superior cms of the subcutaneous inguinal 
ring is attached. The medial border is articular; it is oval, and is marked by eight 
or nine transverse ridges, or a series of nipple-like processes arranged in rows, 
separated by grooves; they serve for the attachment of a thin layer of cartilage, 
which intervenes between it and the interpubic fibrocartilaginous lamina. The 
lateral border presents a sharp margin, the obtinator crest, which forms part of the 
circumference of the obturator foramen and affords attachment to the obturator 
membrane. 

The Lateral Portion of the ascending ramus has three surfaces: superior, inferior, 
and posterior. The superior surface presents a continuation of the pectineal line, 
already mentioned as commencing at the pubic tubercle. In front of this line, the 
surface of bone is triangular in form, wider laterally than medially, and is covered 
by the Pectineus. The surface is bounded, laterally, by a rough eminence, the 
iliopectineal eminence, which serves to indicate the point of junction of the ilium 
and pubis, and below by a prominent ridge which extends from the acetabular 
notch to the pubic tubercle. The inferior surface forms the upper boundary of 
the obturator forailien, and presents, laterally, a broad and deep, oblique groove, 
for the passage of the obturator vessels and nerve; and medially, a sharp margin, 
the obturator crest, forming part of the circumference of the obturator foramen, 
and giving attachment to the obturator membrane. The posterior surface consti- 



I 



THE HIP BONE 237 

tutes part of the anterior boundary of the lesser pelvis. It is smooth, convex from 
above downward, and affords origin to some fibers of the Obturator intornus. 

The Inferior Ramus {ramus infer ior oss. pubis; descending rmnus) .—The inferior 
ramus is thin and flattened. It passes lateralward and downward from the medial 
end of the superior ramus; it becomes narrower as it descends and joins with the 
inferior ramus of the ischium below the obturator foramen. Its anterior surface 
is rough, for the origin of muscles — the Gracilis along its medial border, a portion 
of the Obturator externus where it enters into the formation of the obturator 
foramen, and between these two, the Adductores brevis and magnus, the former 
being the more medial. The posterior surface is smooth, and gives origin to the 
Obturator internus, and, close to the medial margin, to the Constrictor urethrjp. 
The medial border is thick, rough, and everted, especially in females. It presents 
two ridges, separated by an intervening space. The ridges extend downward, and 
are continuous with similar ridges on the inferior ramus of the ischium; to the 
external is attached the fascia of Colles, and to the internal the inferior fascia of 
the urogenital diaphragm. The lateral border is thin and sharp, forms part of the 
circumference of the obturator foramen, and gives attachment to the obturator 
membrane. 

The Acetabulum {cotyloid cavity). — The acetabulum is a deep, cup-shaped, hemi- 
spherical depression, directed downward, lateralward, and forward. It is formed 
medially by the pubis, above by the ilium, laterally and below by the ischium; 
a little less than two-fifths is contributed bv the ilium, a little more than two- 
fifths by the ischium, and the remaining fifth by the pubis. It is bounded by a 
prominent uneven rim, which is thick and strong above, and serves for the attach- 
ment of the glenoidal labrum (cotyloid ligament), which contracts its orifice, and 
deepens the surface for articulation. It presents below a deep notch, the acetabular 
notch, which is continuous with a circular non-articular depression, the acetabular 
fossa, at the bottom of the cavity: this depression is perforated by numerous 
apertures, and lodges a mass of fat. The notch is converted into a foramen by 
the transverse ligament; through the foramen nutrient vessels and nerves enter 
the joint; the margins of the notch serve for the attachment of the ligamentum 
teres. The rest of the acetabulum is formed by a curved articular surface, the 
lunate surface, for articulation with the head of the femur. 

The Obturator Foramen {foramen obturatum; thyroid foramen). — The obturator 
foramen is a large aperture, situated between the ischium and pubis. In the male 
it is large and of an oval form, its longest diameter slanting obliquely from before 
backward; in the female it is smaller, and more triangular. It is bounded by a 
thin, uneven margin, to which a strong membrane is attached, and presents, 
superiorly, a deep groove, the obturator groove, which runs from the pelvis obliquely 
medialward and downward. This groove is converted into a canal by a ligamentous 
band, a specialized part of the obturator membrane, attached to two tubercles: 
one, the posterior obturator tubercle, on the medial border of the ischium, just in 
front of the acetabular notch; the other, the anterior obturator tubercle, on the 
obturator crest of the superior ramus of the pubis. Through the canal the 
obturator vessels and nerve pass out of the pelvis. 

Structure.— The thicker parts of the bone consist of cancellous tissue, enclosed between two 
layers of compact tissue; the thinner parts, as at the bottom of the acetabulum and center of 
the iliac fossa, are usually semitransparent, and composed entirely of compact tissue. 

Ossification (Fig. 237).— The hip bone is ossified from eight centers: three primary— one each 
for the ihum, ischium, and pubis; and five secondary — one each for the crest of the ilium, the 
anterior inferior spine (said to occur more frequently in the male than in the female), the tuberosity 
of the ischium, the pubic symphysis (more frequent in the female than in the male), and one or 
more for the Y-shaped piece at the bottom of the acetabulum. The centers appear in the follow- 
ing order: in the lower part of the ihum, immediately above the greater sciatic notch, about 
the eighth or ninth week of fetal life; in the superior ramus of the ischium, about the third month; 



238 



OSTEOLOGY 



in the superior ramus of the pubis, between the fourth and fifth months. At birth, the three 
primary centers are quite separate, the crest, the bottom of the acetabulum, the ischial tuberosity, 
and the inferior rami of the ischium and pubis being still cartilaginous. By the seventh or eighth 
year, the inferior rami of the pubis and ischium are almost completely united by bone. About 
the thirteenth or fourteenth year, the three primary centers have extended their growth into the 
bottom of the acetabulum, and are there separated from each other by a Y-shaped portion of 
cartilage, which now presents traces of ossification, often by two or more centers. One of these, 
the OS acetabuli, appears about the age of twelve, between the ilium and pubis, and fuses with them 
about the age of eighteen; it forms the pubic part of the acetabulum. The iUum and ischium 
then become joined, and lastly the pubis and ischium, through the intervention of this Y-shaped 
portion. At about the age of puberty, ossification takes place in each of the remaining portions, 
and they join with the rest of the bone between the twentieth and twenty-fifth years. Separate 
centers are frequently found for the pubic tubercle and the ischial spine, and for the crest and 
angle of the pubis. 

Articulations. — The hip bone articulates with its fellow of the opposite side, and with the 
sacrum and femur. 

By eight centers \ ^J"'^^ Wirmry {Ilium. Ischium, and Pubis) 
" •' I Five secondary 



C '-c^^ 




7Tuh 



Fig. 237. — Plao of ossification of the hip bone. The three primary centers unite through a Y-shaped piece about 
puberty. Epiphyses appear about puberty, and unite about twenty-fifth year. 



The Pelvis. 

The pelvis, so called from its resemblance to a basin, is a bony ring, interposed 
between the movable vertebrae of the vertebral column which it supports, and the 
lower limbs upon which it rests; it is stronger and more massively constructed 
than the wall of the cranial or thoracic cavities, and is composed of four bones: 
the two hip bones laterally and in front and the sacrum and coccyx behind. 

The pelvis is divided by an oblique plane passing through the prominence of 
the sacrum, the arcuate and pectineal lines, and the upper margin of the symphysis 
pubis, into the greater and the lesser pelvis. The circumference of this plane is 
termed the linea terminalis or pelvic brim. 

The Greater or False Pelvis {yehis major). — The greater pelvis is the expanded 
portion of the cavity situated above and in front of the pelvic brim. It is bounded 
on either side by the ilium; in front it is incomplete, presenting a wide interval 
between the anterior borders of the ilia, which is filled up in the fresh state by 



THE PELVIS 



239 



the parietes of the abdomen; behind is a deep notch on either side between the ilium 
and the base of the sacrum. It supports the intestines, and transmits part of their 
weight to the anterior wall of the abdomen. 

The Lesser or True Pelvis (pelvis minor)— The lesser pelvis is that part of the 
pelvic cavity which is situated below and behind the pelvic brim. Its bony walls 
are more complete than those of the greater pelvis. For convenience of descrip- 
tion, it is divided into an_ inlet bounded by tlie superior circumference, and outlet 
bounded by the inferior circumference, and a cavity. 

The Superior Circumference.— The superior circumference forms the brim of the 
pelvis, the included space being called the superior aperture or inlet (apertura pelvis 
[minoris] superior) (Fig. 238). It is formed laterally by the pectineal and arcuate 
lines, in front by the crests of the pubes, and behind by the anterior margin of the 
base of the sacrum and sacrovertebral angle. The superior aperture is somewhat 
heart-shaped, obtusely pointed in front, diverging on either side, and encroached 
upon behind by the projection forward of the promontory of the sacrum. It has 
three principal diameters: antero-posterior, transverse, and oblique. The antero- 
posterior or conjugate diameter extends from the sacrovertebral angle to the sym- 




Fig. 238. — Diameters of .superior aperture of lesser pelvis (female). 

physis pubis; its average measurement is about 110 mm. in the female. The 
transverse diameter extends across the greatest width of the superior aperture, 
from the middle of the brim on one side to the same point on the opposite; its aver- 
age measurement is about 135 mm. in the female. The oblique diameter extends 
from the iliopectineal eminence of one side to the sacroiliac articulation of the 
opposite side; its average measurement is about 125 mm. in the female. 

The cavity of the lesser pehis is bounded in front and below b}'- the pubic sym- 
physis and the superior rami of the pubes ; above and behind, by the pelvic surfaces 
of the sacrum and coccyx, which, curving forward above and below, contract 
the superior and inferior apertures of the cavity; laterally, by a broad, smooth, 
quadrangular area of bone, corresponding to the inner surfaces of the body and 
superior ramus of the ischium and that part of the ilium which is below the arcuate 
line. From this description it will be seen that the cavity of the lesser pelvis 
is a short, curved canal, considerably deeper on its posterior than on its anterior 
wall. It contains, in the fresh subject, the pelvic colon, rectum, bladder, and some 
of the organs of generation. The rectum is placed at the back of the pelvis, in 
the curve of the sacrum and coccyx; the bladder is in front, behind the pubic sym- 
physis. In the female the uterus and vagina occupy the interval between these viscera. 



240 



OSTEOLOGY 



The Lower Circumference.^The lower circumference of the pelvis is very irregular; 
the space enclosed by it is named the inferior aperture or outlet (apertura pelvis 
[minoris] inferior) (Fig. 239), and is bounded behind by the point of the coccjtc, 
and laterally by the ischial tuberosities. These eminences are separated by three 
notches: one in front, the pubic arch, formed by the convergence of the inferior 




Fig. 239. — Diameters of inferior aperture of lesser pelvis (female). 



rami of the ischium and pubis on either side. The other notches, one on either 
side, are formed by the sacrum and coccyx behind, the ischium in front, and 
the ilium above; they are called the sciatic notches; in the natural state they are 
converted into foramina by the sacrotuberous and sacrospinous ligaments. When 
the ligaments are in situ, the inferior aperture of the pelvis is lozenge-shaped, 

bounded, in front, by the pubic arcuate ligament 
and the inferior rami of the pubes and ischia; later- 
ally, by the ischial tuberosities; and behind, by the 
sacrotuberous ligaments and the tip of the coccyx. 

The diameters of the outlet of the pelvis are two, 
antero-posterior and transverse. The antero-posterior 
diameter extends from the tip of the coccyx to the 
lower part of the pubic symphysis; its measurement 
is from 90 to 115 mm. in the female. It varies with 
the length of the coccyx, and is capable of increase 
or diminution, on account of the mobility of that 
bone. The transverse diameter, measured between 
the posterior parts of the ischial tuberosities, is about 
115 mm. in the female. ^ 

Axes (P'ig. 240). — A line at right angles to the plane 
of the superior aperture at its center would, if prolonged, 
pass through the umbilicus above and the middle 
of the coccyx below ; the axis of the superior aperture 
is therefore directed downward and backward. The 
axis of the inferior aperture, produced upward, would 
touch the base of the sacrum, and is also directed 
downward, and slightly backward. The axis of the cavity — i. e., an axis at right 
angles to a series of planes between those of the superior and inferior apertures 

1 The measurements of the pehns given above are fairly accurate, but different figures are given by various authors 
no doubt due mainly to differences in the physique and stature of the population from whom the measurements have 
been taken. 




Fio. 



240. — Median sagittal section of 
pelvis. 



THE PELVIS 



241 



— is curved like the cavity itself: this curve corresponds to the concavity of the 
sacrum and coccyx, the extremities being indicated by the central points of the 
superior and inferior apertures. A knowledge of the direction of these axes 
serves to explain the course of the fetus in its passage through the pelvis during 
parturition. 

Position of the Pelvis (Fig. 240).— In the erect posture, the pelvis is placed 
obliquely with regard to the trunk: the plane of the superior aperture forms an 
angle of from 50° to 60°, and that of the inferior aperture one of about 15° with 
the horizontal plane. The pelvic surface of the symphysis pubis looks upward 
and backward, the concavity of the sacrum and coccyx downward and forward. 
The position of the pelvis in the erect posture may be indicated by holding it so 
that the anterior superior iliac spines and the front of the top of the symphysis 
pubis are in the same vertical plane. 




Fia. 241. — Male pelvis. 

Differences between the Male and Female Pelves. — The female pelvis (Fig. 
242) is distinguished from that of the male (Fig. 241) by its bones being more 
delicate and its depth less. The whole pehis is less massive, and its muscular 
impressions are slightly marked. The ilia are less sloped, and the anterior iliac 
spines more widely separated; hence the greater lateral prominence of the hips. 
The preauricular sulcus is more commonly present and better marked. The supe- 
rior aperture of the lesser pelvis is larger in the female than in the male; it is more 
nearly circular, and its obliquity is greater. The cavity is shallower and wider; 
the sacrum is shorter Avider, and its upper part is less curved; the obturator 
foramina are triangular in shape and smaller in size than in the male. The inferior 
aperture is larger and the coccyx more movable. The sciatic notches are wider 
and shallower, and the spines of the ischia project less inward. The acetabula 
are smaller and look more distinctly forward (Derry^). The ischial tuberosities 
and the acetabula are wider apart, and the former are more everted. The pubic 
symphysis is less deep, and the pubic arch is wider and more rounded than in the 
male, Avhere it is an angle rather than an arch. 



> Journal of .\natomy and Physiology, vol. xliii. 



16 



242 



OSTEOLOGY 



The size of the pelvis varies not only in the two sexes, but also in different 
members of the same sex, and does not appear to be influenced in any way by the 
height of the individual. Women of short stature, as a rule, have broad pelves. 
Occasionally the pelvis is equally contracted in all its dimensions, so much so 
that all its diameters measure 12.5 mm. less than the average, and this even in 
well-formed women of average height. The principal divergences, however, are 
found at the superior aperture, and affect the relation of the antero-posterior 
to the transverse diameter. Thus the superior aperture may be elliptical either 
in a transverse or an antero-posterior direction, the transverse diameter in the 
former, and the antero-posterior in the latter, greatly exceeding the other diameters; 
in other instances it is almost circular. 




Fig. 242. — Female pelvis. 

In the fetus, and for several years after birth, the pelvis is smaller in proportion 
than in the adult, and the projection of the sacrovertebral angle less marked. 
The characteristic differences between the male and female pelvis are distinctly 
indicated as early as the fourth month of fetal life. 

Abnormalities. — There is arrest of development in the bones of the pelvis in cases of extro- 
version of the bladder; the anterior part of the pelvic girdle is deficient, the superior rami of 
the pubes are imperfectly developed, and the symphysis is absent. "The pubic bones are sepa- 
rated to the extent of from two to four inches, the superior rami shortened and directed forward, 
and the obturator foramen diminished in size, narrowed, and turned outward. The iliac bones 
are straightened out more than normal. The sacrum is very peculiar. The lateral curve, instead 
of being concave, is flattened out or even convex, with the iliosacral facets turned more outward 
than normal, while the vertical curve is straightened."^ 



The Femur (Thigh Bone). 

The femur (Figs. 244, 245), the longest and strongest bone in the skeleton, is 
almost perfectly cylindrical in the greater part of its extent. In the erect posture 
it is not vertical, being separated above from its fellow by a considerable interval, 
which corresponds to the breadth of the pelvis, but inclining gradually downward 
and medialward, so as to approach its fellow toward its lower part, for the purpose 
of bringing the knee-joint near the line of gravity of the body. The degree of this 
inclination varies in different persons, and is greater in the female than in the male, 

> Wood, Heath's Dictionary of Practical Surgery, i, 426. 



THE FEMUR 



243 



on account of the greater breadth of the pelvis. The femur, like other long bones, 
is divisible into a body and two extremities. 

The Upper Extremity (proxiinal extremity, Fig. 243).— The upper extremity 
presents for examination a head, a neck, a greater and a lesser trochanter. 

The Head {caput femoris) .—The head which is globular and forms rather more 
than a hemisphere, is directed upward, medialward, and a little forward, the greater 
part of its convexity being above and in front. Its surface is smooth, coated with 
cartilage in the fresh state, except over an ovoid depression, the fovea capitis 
femoris, which is situated a little below and behind the center of the head, and gives 
attaclmient to the ligamentum teres. 

The Neck {collum femoris).— The neck is a flattened pyramidal process of bone, 
connecting the head with the body, and forming with the latter a wide angle open- 
ing medialward. The angle is wildest in infancy, and becomes lessened during 
growth, so that at puberty it forms a gentle curve from the axis of the body of the 
bone. In the adult, the neck forms an angle of about 125° with the body, but this 
varies in inverse proportion to the development of the pelvis and the stature. In 

Obturator internus and Oemelli 
Piriformis 

Insertion of Obturator 



Fovea capitis, 
Jor lig, teres 



, t, j^^ T-r ■ Cheater trochanter 




externus 



Lesser trochanter 



Fio. 243. — Upper extremity of right femur viewed from behind and above. 



the female, in consequence of the increased width of the pelvis, the neck of the 
femur forms more nearly a right angle with the body than it does in the male. 
The angle decreases during the period of growth, but after full growth has been 
attained it does not usually undergo any change, even in old age; it varies con- 
siderably in different persons of the same age. It is smaller in short than in long 
bones, and when the pelvis is wide. In addition to projecting upward and medial- 
ward from the body of the femur, the neck also projects somewhat forward ; the 
amount of this forw^ard projection is extremely variable, but on an average is from 
12° to 14°. 

The neck is flattened from before backward, contracted in the middle, and 
broader laterally than medially. The vertical diameter of the lateral half is in- 
creased by the obliquity of the lower edge, which slopes downward to join the 
body at the level of the lesser trochanter, so that it measures one-third more 
than the antero-posterior diameter. The medial half is smaller and of a more 
circular shape. The anterior sm-face of the neck is perforated by numerous vascular 
foramina. Along the upper part of the line of junction of the anterior surface 
with the head is a shallow groove, best marked in elderly subjects; this 



244 



OSTEOLOGY 



Obturator internus 
and Gemelli 
Piriformis 



Tubercle 



Articular capsule 




Artictdar capsule 



Adductor 
tubercle 



Medial 
ejncondylc 



""^ Con<ll}^ 



"'^^l/Je 



Fig. 244. — Right femur. Anterior surface. 



groove lodges the orbicular fibers 
of the capsule of the hip-joint. 
The posterior surface is smooth, and 
is broader and more concave than 
the anterior: the posterior part of 
the capsule of the hip-joint is 
attached to it about 1 cm. above 
the intertrochanteric crest. The 
superior border is short and thick, 
and ends laterally at the greater 
trochanter; its surface is perforated 
by large foramina. The inferior 
border, long and narrow, curves a 
little backward, to end at the lesser 
trochanter. 

The Trochanters. — The trochan- 
ters are prominent processes which 
afford leverage to the muscles that 
rotate the thigh on its axis. They 
are two in number, the greater and 
the lesser. 

The Greater Trochanter {trochanter 
major; great trochanter) is a large, 
irregular, quadrilateral eminence, 
situated at the junction of the neck 
with the upper part of the body. It 
is directed a little lateralward and 
backward, and, in the adult, is about 
1 cm. lower than the head. It has 
two surfaces and four borders. The 
lateral surface, quadrilateral in form, 
is broad, rough, convex, and marked 
by a diagonal impression, which 
extends from the postero-superior 
to the antero-inferior angle, and 
serves for the insertion of the ten- 
don of the Cilutteus medius. Above 
the impression is a triangular sur- 
face, sometimes rough for part of 
the tendon of the same muscle, 
sometimes smooth for the inter- 
position of a bursa between the 
tendon and the bone. Below and 
behind the diagonal impression is 
a smooth, triangular surface, over 
which the tendon of the Gluteus 
maximus plays, a bursa being inter- 
posed. The medial surface, of much 
less extent than the lateral, pre- 
sents at its base a deep depression, 
the trochanteric fossa {digital fossa) , 
for the insertion of the tendon of 
the Obturator externus, and above 
and in front of this an impression 
for the insertion of the Obtura- 



THE FEMUR 



245 



tor internus and Gemelli. The 
superior border is free ; it is thick 
and irregular, and marked near 
the center by an impression for 
the insertion of the Piriformis. 
The inferior border corresponds 
to the Hne of junction of the 
base of the trochanter with the 
lateral surface of the body; it is 
marked by a rough, prominent, 
slightly curved ridge, which gives 
origin to the upper part of the 
Vastus lateralis. The anterior 
border is prominent and some- 
what irregular; it afl'ords inser- 
tion at its lateral part to the 
Glutieus minimus. The posterior 
border is very prominent and 
appears as a free, rounded edge, 
which bounds the back part of 
the trochanteric fossa. 

The Lesser Trochanter (tro- 
chanter minor; small trochanter) 
is a conical eminence, which 
varies in size in different sub- 
jects; it projects from the lower 
and back part of the base of the 
neck. From its apex three well- 
marked borders extend; two of 
these are above — a medial con- 
tinuous with the lower border 
of the neck, a lateral with the 
intertrochanteric crest; the in- 
ferior border is continuous with 
the middle division of the linea 
aspera. The summit of the tro- 
chanter is rough, and gives in- 
sertion to the tendon of the 
Psoas major. 

A prominence, of variable size, 
occurs at the junction of the 
upper part of the neck with the 
greater trochanter, and is called 
the tubercle of the femur; it is 
the point of meeting of five 
muscles: the Glut^-us minimus 
laterally, the Vastus lateralis 
below, and the tendon of the 
Obturator internus and two 
Gemelli above. Running ob- 
liquely downward and medial- 
ward from the tubercle is the 
intertrochanteric line {spiral line 
of the femur); it winds around 
the medial side of the body of 
the bone, below the lesser tro- 






Articular 
capsule 




Lateral 
epicoiidyle 

Groove for 
tendon of 
Popliteus 



TTrt^ 



Fig. 245. 



Articular 
capsule 
-Right femur. 



Posterior surface. 



246 OSTEOLOGY 

chanter, and ends about 5 cm. below this eminence in the linea aspera. Its upper 
half is rough, and affords attachment to the iliofemoral ligament of the hip-joint; 
its lower half is less prominent, and gives origin to the upper part of the Vastus 
medialis. Running obliquely downward and medialward from the summit of the 
greater trochanter on the posterior surface of the neck is a prominent ridge, the 
intertrochanteric crest. Its upper half forms the posterior border of the greater tro- 
chanter, and its lower half runs downward and medialward to the lesser trochanter. 
A slight ridge is sometimes seen commencing about the middle of the intertrochan- 
teric crest, and reaching vertically downward for about 5 cm. along the back part 
of the body: it is called the linea quadrata, and gives attachment to the Quad- 
ratus femoris and a few fibers of the Adductor magnus. Generally there is merely 
a slight thickening about the middle of the intertrochanteric crest, marking the 
attachment of the upper part of the Quadratus femoris. 

The Body or Shaft (cor pm femoris). — The body, almost cylindrical in form, is 
a little broader above than in the center, broadest and somewhat flattened from 
before backward below. It is slightly arched, so as to be convex in front, and con- 
cave behind, where it is strengthened by a prominent longitudinal ridge, the linea 
aspera. It presents for examination three borders, separating three surfaces. Of 
the borders, one, the linea aspera, is posterior, one is medial, and the other, lateral. 

The linea aspera (Fig. 245) is a prominent longitudinal ridge or crest, on the 
middle third of the bone, presenting a medial and a lateral lip, and a narrow 
rough, intermediate line. Above, the linea aspera is prolonged by three ridges. 
The lateral ridge is very rough, and runs almost vertically upward to the base of 
the greater trochanter. It is termed the gluteal tuberosity, and gives attachment 
to part of the Gluteus maximus : its upper part is often elongated into a roughened 
crest, on which a more or less well-marked, rounded tubercle, the third trochanter, 
is occasionally developed. The intermediate ridge or pectineal line is continued 
to the base of the lesser trochanter and gives attachment to the Pectineus; the 
medial ridge is lost in the intertrochanteric line; between these two a portion of the 
Iliacus is inserted. Below, the linea aspera is prolonged into two ridges, enclosing 
between them a triangular area, the popliteal surface, upon which the popliteal 
artery rests. Of these two ridges, the lateral is the more prominent, and descends 
to the summit of the lateral condyle. The medial is less marked, especially at its 
upper part, where it is crossed by the femoral artery. It ends below at the summit 
of the medial condyle, in a small tubercle, the adductor tubercle, which affords 
insertion to the tendon of the Adductor magnus. 

From the medial lip of the linea aspera and its prolongations above and below, 
the Vastus medialis arises; and from the lateral lip and its upward prolongation, 
the Vastus lateralis takes origin. The Adductor magnus is inserted into the linea 
aspera, and to its lateral prolongation above, and its medial prolongation below. 
Between the Vastus lateralis and the Adductor magnus two muscles are attached 
— viz., the Glutams maximus inserted above, and the short head of the Biceps 
femoris arising below. Betweeen the Adductor magnus and the Vastus medialis 
four muscles are inserted: the Iliacus and Pectineus above; the Adductor brevis 
and Adductor longus below. The linea aspera is perforated a little below its center 
by the nutrient canal, which is directed obliquely upward. 

The other two borders of the femur are only slightly marked: the lateral border 
extends from the antero-inferior angle of the greater trochanter to the anterior 
extremity of the lateral condyle; the medial border from the intertrochanteric line, 
at a point opposite the lesser trochanter, to the anterior extremity of the medial 
condyle. 

The anterior surface includes that portion of the shaft which is situated between 
the lateral and medial borders. It is smooth, convex, broader above and below 
than in the center. From the upper three-fourths of this surface the ^^astus inter- 
medius arises; the lower fourth is separated from the muscle by the intervention 



THE FEMUR 



247 



of the synovial membrane of the knee-joint and a bursa; from the upper part of it 
the ArticuL^ris genu takes origin. The lateral surface includes the portion between 
the lateral border and the linea aspera; it is continuous above with the correspond- 
ing surface of the greater trochanter, below with that of the lateral condyle: from 
its upper three-fourths the Vastus intermedins takes origin. The medial surface 
includes the portion between the medial border and the linea aspera; it is continu- 
ous above with the lower border of the neck, below with the medial side- of the 
medial condyle: it is covered by the Vastus medialis. 

The Lower Extremity {distal extremity), (Fig. 246).— The lower extremity, larger 
than the upper, is somewhat cuboid in form, but its transverse diameter is greater 
than its antero-posterior; it consists of two oblong eminences known as the condyles. 
In front, the condyles are but slightly prominent, and are separated from one another 
by a smooth shallow articular depression called the patellar surface; behind, they 
project considerably, and the interval between them forms a deep notch, the 
intercondyloid fossa. The lateral condyle is the more prominent and is the broader 
both in its antero-posterior and transverse diameters, the medial condyle is the 
longer and, when the femur is held with its body perpendicular, projects to a lower 



Lateral groove — «f 

i 

Lateral epicondyle-*^^ 




Medial groove 



Medial epicondyle 
Semilunar area 



I 



Fig. 246. — Lower extremity of right femur viewed from below. 

level. When, however, the femur is in its natural oblique position the lower sur- 
faces of the two condyles lie practically in the same horizontal plane. The condyles 
are not quite parallel with one another; the long axis of the lateral is almost 
directly antero-posterior, but that of the medial runs backward and medialward. 
Their opposed surfaces are small, rough, and concave, and form the walls of the 
intercondyloid fossa. This fossa is limited above by a ridge, the intercondyloid 
line, and below by the central part of the posterior margin of the patellar surface. 
The posterior cruciate ligament of the knee-joint is attached to the lower and front 
part of the medial wall of the fossa and the anterior cruciate ligament to an impres- 
sion on the upper and back part of its lateral wall. Each condyle is surmounted 
by an elevation, the epicondyle. The medial epicondyle is a large convex eminence 
to which the tibial collateral ligament of the knee-joint is attached. At its upper 
part is the adductor tubercle, already referred to, and behind it is a rough impres- 
sion which gives origin to the medial head of the Gastrocnemius. The lateral 
epicondyle, smaller and less prominent than the medial, gives attachment to the 
fibular collateral ligament of the knee-joint. Directly below it is a small depression 
from which a smooth well-marked groove curves obliquely upward and backward 
to the posterior extremity of the condyle. This groove is separated from the 
articular surface of the condyle by a prominent lip across which a second, shallower 
groove runs \'ertically downward from the depression. In the fresh state these 
grooves are covered with cartilage. The Popliteus arises from the depression; 
its tendon lies in the oblique groove when the knee is flexed and in the vertical 



248 OSTEOLOGY 

groove when the knee is extended. Above and behind the lateral epicondyle is 
an area for the origin of the lateral head of the Gastrocnemius, above and to the 
medial side of which the Plantaris arises. 

The articular surface of the lower end of the femur occupies the anterior, inferior, 
and posterior surfaces of the condyles. Its front part is named the patellar surface 
and articulates with the patella; it presents a median groove which extends down- 
ward to the intercondyloid fossa and two convexities, the lateral of which is broader, 
more prominent, and extends farther upward than the medial. The lower and 
posterior parts of the articular surface constitute the tibial surfaces for articulation 
with the corresponding condyles of the tibia and menisci. These surfaces are 
separated from one another by the intercondyloid fossa and from the patellar 
surface by faint grooves which extend obliquely across the condyles. The lateral 
groove is the better marked; it runs lateralward and forward from the front part 
of the intercondyloid fossa, and expands to form a triangular depression. When 
the knee-joint is fully extended, the triangular depression rests upon the anterior 
portion of the lateral meniscus, and the medial part of the groove comes into con- 
tact with the medial margin of the lateral articular surface of the tibia in front 
of the lateral tubercle of the tibial intercondyloid eminence. The medial groove 
is less distinct than the lateral. It does not reach as far as the intercondyloid 
fossa and therefore exists only on the medial part of the condyle; it receives the 
anterior edge of the medial meniscus when the knee-joint is extended. Where the 
groove ceases laterally the patellar surface is seen to be continued backward as 
a semilunar area close to the anterior part of the intercondyloid fossa; this semi- 
lunar area articulates with the medial vertical facet of the patella in forced flexion 
of the knee-joint. The tibial surfaces of the condyles are convex from side to side 
and from before backward. Each presents a double curve, its posterior segment 
being an arc of a circle, its anterior, part of a cycloid.^ 

The Architecture of the Femur. — Koch^ ]\v mathematical analysis has "shown that in every 
part of the femur there is a remarkable adaptation of the inner structure of the bone to the machan- 
ical requirements due to the load on the femur-head. The various parts of the femur taken 
together form a single mechanical structure wonderfully well-adapted for the efficient, economical 
transmission of the loads from the acetabulum to the tibia; a structure in which every element 
contributes its modicum of strength in the manner required by theoretical mechanics for maximum 
efficiency." "The internal structure is everywhere so formed as to provide in an efficient manner 
for all the internal stresses which occur due to the load on the femur-head. Throughout the femur, 
with the load on the femur-head, the bony material is arranged in the paths of the maximum 
internal stresses, which are thereby resisted with the greatest efficiency, and hence with maximum 
economy of material." "The conclusion is inevitable that the inner structure and outer form of 
the femur are governed by the conditions of maximum stress to which the bone is subjected 
normally by the preponderant load on the femur-head; that is, by the body weight transmitted 
to the femur-head through the acetabulum." "The femur obeys the mechanical laws that govern 
other elastic bodies under stress; the relation between the computed internal stresses due to the 
load on the femur-head, and the internal structure of the different portions of the femur is in very 
close agreement with the theoretical relations that should exist between stress and structure for 
maximum economy and efficiency; and, therefore, it is believed that the following laws of bone 
structure have been demonstrated for the femur: 

"1. The inner structure and external form of human bone are closely adapted to the mechanical 
conditions existing at every point in the bone. 

"2. The inner architecture of normal bone is determined by definite and exact requirements of 
mathematical and mechanical laws to produce a maximum of strength with a minimum of 
material." 

The Inner Architecture of the Upper Femur.— "The spongy l)one of the upper femur (to the 
lower limit of the lesser trochanter) is composed of two distinct systems of trabecule arranged in 
curved paths: one, which has its origin in the medial (inner) side of the shaft and curving upward 

' A cycloid is a curve traced bj' a point in the circumference of a wheel when tlie wlieel is rolled along in a straight 
line. 

2 The Laws of Bone Architecture. Am. Jour, of .\nat., 21, 1917. The following paragraphs are taken almost ver- 
batum from Koch's article in which we have the first correct mathematical analysis of the femur in support of the 
theory of the functional form of bone proposed by Wolff and also by Roux. 



THE FEMUR 



249 



in a fan-like radiation to the oppoaite side of the bone; the other, having origin in the later d 
(outer) portion of the shaft and arching upward and medially to end in th! upper surface of the 

^"TMT^:ur' ""' '" '.'^'^ ^)Z 'r ^^^^^"^ -^--^^ -^h other a7St angles ' 

; f !1 f f «^?^^^f«"t^ System of Trabeculce.~As the compact bone of fhe medial (inner) 

part of the shaft nears the head of the femur it gradually becomes thinner and finally reaches the 

articular surface of the head as a very thin layer. From a point at about the lower level of he 




Fig. 217. — Frontal longitudinal midsection of upptr femur. 



lesser trochanter, 2^ to 3 inches from the lower limit of the articular surface of the head, the 
trabeculae branch off from the shaft in smooth curves, spreading radially to cross to the opposite 
side in two well-defined groups: a lower, or secondary group, and an upper, or principal group. 

"a. The Secondary Compressive Group. — This group of trabecular leaves the inner border of the 
shaft beginning at about the level of the lesser trochanter, and for a distance of almost 2 inches 
along the curving shaft, with which the separate trabeculae make an angle of about 15 degrees. 



250 



OSTEOLOGY 



They curve outwardly and upwardly to cross in radiating smooth curves to the opposite side. 
The lower filaments end in the region of the greater trochanter: the adjacent filaments above 
these pursue a more nearly vertical course and end in the upper portion of the neck of the femur. 
The trabecula; of this group are thin and with wide spaces between them. As they traverse 
the space between the medial and lateral surfaces of the bone they cross at right angles the system 
of curved trabeculae which arise from the lateral (outer) portion of the shaft. (Figs. 247 and 249.) 
"b. The Principal Compressive Group. — This group of trabeculse (Figs. 247 and 249) springs 
from the medial portion of the shaft just above the group above-described, and spreads upward 
and in slightly radial smooth curved lines to reach the upper portion of the articular surface of 
the head of the femur. These trabecule are placed very closely together and are the thickest ones 
seen in the upper femur. They are a prolongation of the shaft from which they spring in straight 

LOAD 




Fig. 248. — Diagram of the lines of stress in the upper femur, based upon the mathematical analysis of the right 
femur. These result from the combination of the different kinds of stresses at each point in the femur. (After 
Koch ) 



lines which gradually curve to meet at right-angles the articular surface. There is no change as 
they cross the epiphyseal line. They also intersect at right-angles the system of lines which rise 
from the lateral side of the femur. 

"This system of principal and secondary compressive trabeculse corresponds in position and in 
curvature with the lines of maximum compressive stress, which were traced out in the mathematical 
analysis of this portion of the femur. (Figs. 247 and 250.) 

"B. Lateral (Tensile) System of Traheculce. — As the compact bone of the outer portion of the 
shaft approaches the greater trochanter it gradually decreases in thickness. Beginning at a point 
about 1 inch below the level of the lower border of the greater trochanter, nimierous thin trabeculse 
are given off from the outer portion of the shaft. These trabeculse lie in three distinct groups. , 

"c. The Greater Trochanter Group. — These trabeculai rise from the outer part of the shaft just 
below the greater trochanter and rise in thin, curving lines to cross the region of the greater 
trochanter and end in its upper surface. Some of these filaments are poorly defined. This group 



THE FEMUR 



251 





Fig. 249. — Frontal longitudinal midsection of left 
femur. Taken from the same subject as the one that 
was analyzed and shown in Figs. 248 and 250. i of 
natural size, (.\fter Koch.) 



Fig. 250. — Diagram of the computed lines of 
maximum stress in the normal femur. The section 
numbers 2, 4, 6 , 8, etc., show the positions of the 
transverse sections analyzed. The amounts of the 
maximum tensile and compressive stress at the 
various sections are given for a load of 100 pounds on 
the femur-head. For the standing position ("at at- 
tention") these stresses are multiplied by 0.6, for 
walking by 1.6 and for running by 3.2. (After Koch.) 



252 



OSTEOLOGY 



intersects the trabeculiB of group (a) which rise from the opposite side. The trabeculse of this 
group evidenth' carry small stresses, as is shown by their slenderness. 

"d. The Principal Tensile Group. — This group springs from the outer part of the shaft imme- 
diately below group c, and curves convexly upward and inward in nearly parallel lines across the 
neck of the femur and ends in the inferior portion of the head. These trabecuiae are somewhat 
thinner and more widely spaced than those of the principal compressive group (b). All the trabec- 
ula? of this group cross those of groups (a) and (b) at right angles. This group is the most impor- 
tant of the lateral system (tensile) and, as will be sho^NTi later, the greatest tensile stresses of the 
upper femur are carried bj^ the trabecuiae of this group. 

"e. The Secondary Tensile Group. — This group consists of the trabecular which spring from the 
outer side of the shaft and lie below those of the preceding group. They curve upward and medially 
across the axis of the femur and end more or less irregularly after crossing the midline, but a 
nimiber of these filaments end in the medial portion of the shaft and neck. They cross at right 
angles the trabecuiae of group (o). 




Fig. 251. 



O = C0MPRESSI0N 

• = TENS10N 
C=COMP. & TENSION 
NEUTRAL AXTS 



-Intensity of the maximum tensile and compressive stresses in the upper femur. Computed for the load of 
100 pounds on the right femur. Corresponds to the upper part of Fig. 250. (After Koch.) 



"In general, the trabecula? of the tensile system are lighter in structure than those of the com- 
pressive system in corresponding positions. The significance of the difference in thickness of these 
two systems is that the thickness of the trabecuiae varies with the intensity of the stresses at any 
given point. Comparison of Fig. 247 with Fig. 251 will show that the trabecular of the com- 
pressive system carry heavier stresses than those of the tensile sj'stem in corresponding positions. 
For example, the maximum tensile stress at section 8 (Fig. 251) in the outermost fiber is 771 
pounds per square inch, and at the corresponding point on the compressive side the compressive 
stress is 954 pounds per square inch. Similar comparisons may be made at other points, which 
confirm the conclusion that the thickness and closeness of spacing of the trabecuiae varies in 
proportion to the intensity of the stresses carried by them. 

"It will be seen that the trabecuiae lie exactly in the paths of the maximum tensile and com- 
pressive stresses (compare Figs. 247, 248 and 251), and hence these trabecula? carry these stresses 
in the most economical manner. This is in accordance with the well-recognized principle of 
mechanics that the most direct manner of transmitting stress is in the direction in which the stress 
acts. 



THE FEMUR 253 

"Fig. 249 shows a longitudinal frontal section through the left femur, which is the mate of the 
right femur on which the mathematical analysis was made. In this midsection the sy.stom of 
tensile trabecule, which rises from the lateral (outer) part of the shaft and crosses over the central 
area to end in the medial portion of the shaft, neck and head, is clearly shown. This figun* also 
shows the compressive system of trabecular which rises on the medial portion of the shaft and 
crosses the central area to end in the head, neck and greater trochanter. By comparing th(; posi- 
tion of these two systems of trabecule shown in Fig. 249 with the lines of maximum and minimum 
stresses shown in Figs. 248 and 250 it is seen that the tensile system of trabecuUe corresjwnds 
exactly with the position of the lines of maximum and minimum tensile stresses which were 
determined by mathematical analysis. In a similar manner, the compressive system of trabecuhe 
in Fig. 249 corresponds exactly with the lines of maximum and minimum compressive stresses 
computed by mathematical analysis. 

"The amount of vertical shear varies almost uniformly from a maximum of 90 pounds (90 per 
cent, of the load on the femur-head) midway between sections 4 and 6, to a minimum of — 5.7 
pounds at section 18" (Fig. 251). There is a gradual diminution of the spongy bone from section 
6 to section 18 parallel with the diminished intensities of the vertical shear. 

1. The trabecuke of the upper femur, as shown in frontal sections, are arranged in two general 
systems, compressive and tensile, which correspond in position with the lines of maximum and 
minimum stres.ses in the femur determined by the mathematical analysis of the femur as a mechan- 
ical structiu-e. 

2. The thickness and spacing of the trabeculse vary with the intensity of the maximum stresses 
at various points in the upjier femur, being thickest and most closely spaced in the regions where 
the greatest stresses occur. 

3. The amount of bony material in the spongy bone of the upper femur varies in proportion to 
the intensity of the shearing force at the various sections. 

4. The arrangement of the trabeculse in the positions of maximum stresses is such that the 
greatest strength is secured with a minimum of material. 

Significance of the Inner Architecture of the Shaft. — 1. Economy for resisting shear. The shearing 
stresses are at a minimum in the shaft. "It is clear that a minimum amount of material will be 
required to resist the shearing stresses." As horizontal and vertical shearing stresses are most 
efficiently resisted by material placed near the neutral plane, in this region a minimum amount 
of material wiU be needed near the neutral axis. In the shaft there is very little if any material 
in the central space, practically the only material near the neutral plane being in the compact 
bone, but lying at a distance from the neutral axis. This conforms to the requirement of mechanics 
for economy, as a minimum of material is provided for resisting shearing stresses where these 
stresses are a minimum. 

2. Economy for resisting bending moment. "The bending moment increases from a minimum 
at section 4 to a maximum between sections 16 and 18, then gradually decreases almost uniformly 
to near section 75." "To resist bending moment stresses most effectively the material should 
be as far from the neutral axis as possible." It is evident that the hollow shaft of the femur is 
an efficient structure for resisting bending moment stresses, all of the material in the shaft being 
relatively at a considerable distance from the neutral axis. It is evident that the hollow shaft 
provides efficiently for resisting bending moment not only due to the load on the femur-head, but 
from any other loads tending to produce bending in other planes. 

3. Economy for resisting axial stress. 

The inner architecture of the shaft is adapted to resist in the most efficient manner the com- 
bined action of the minimal shearing forces and the axial and maximum bending stresses. 

The structure of the shaft is such as to secure great strength with a relatively small amount of 
material. 

The Distal Portion of the Femur. — In frontal section (Fig. 249) in the distal 6 inches of the 
femur "there are to be seen two main systems of trabecular, a longitudinal and a transverse 
system. The trabeculip of the former ri.se from the inner wall of the shaft and continue in per- 
fectly straight lines parallel to the axis of the shaft and proceed to the epiphyseal line, whence 
they continue in more or less curved lines to meet the articular surface of the knee-joint at right 
angles at every point. Near the center there are a few thin, delicate, longitudinal trabeculse 
which spring from the longitudinal trabeculse just described, to which they are joined by fine 
transverse filaments that lie in planes parallel to the sagittal plane. 

"The trabeculse of the transverse system are somewhat lighter in structure than those of the 
longitudinal .system, and consist of numerous trabeculie at right angles to the latter. 

"As the distal end of the femur is approached the shaft gradually becomes thinner until the 
articular surface is reached, where there remains only a thin shell of compact bone. With the 
gradual thinning of the compact bone of the shaft, there is a simultaneous increase in the amount 
of the spongy bone, and a gradual flaring of the femur which gives this portion of the bone a 
gradually increasing gross area of cross-section. 

"There is a marked thickening of the shell of bone in the region of the intercondyloid fo.ssa 
where the anterior and posterior crucial ligaments are attached. This thickened area is about 



254 



OSTEOLOGY 



Appears at 

ith year ; 
joins body 
about 18th yr. ^ 



Appears at 

9th month of 

fetal life 




Appears at 
end of 1st yr. ; 

joins body 
about l%th yr. 

Appears IWi-l^th 

year ; joins body 

about 18th year 



Joins body at 
20th year 



Lower extremity 



Fig. 252. — Plan of ossification of the femur, 
five centers. 



From 



0.4 inch in diameter and consists of compact 
bone from which a nimiber of thick trabeculse 
pass at right angles to the main longitudinal 
system. The inner structm-e of the bone is here 
e\'idently adajited to the efficient distribution of 
the stresses arising from this ligamentary at- 
tachment. 

"Near the distal end of the femur the longi- 
tudinal trabecular gradually assume curved 
paths and end perpendicularly to the articular 
surface at every point. Such a structure is in 
accordance with the principles of mechanics, 
as stresses can be communicated through a 
frictionless joint only in a direction perpendic- 
ular to the joint surface at every point. 

"With practically no increase in the amount 
of bony material used, there is a greatly increased 
stability produced by the expansion of the lower 
femur from a hollow shaft of compact bone to a 
structure of much larger cross-section almost 
entirely composed of spongy bone. 

"Significance of the Inner Architecture of the 
Distal Port of the Femur. — The function of the 
lower end of the femur is to transmit through a 
hinged joint the loads carried by the femur. For 
stability the width of the bearing on which the 
hinge action occurs should be relatively large. 
For economy of material the expansion of the end 
bearing should be as lightly constructed as is 
consistent with proper strength. In accordance 
with the ])rinciples of mechanics , 






Fig. 253. — Epiphysial lines of femur in a young 
adult. Anterior aspect. The lines of attachment of 
the articular capsules are in blue. 




Fig. 254. — Epiphysial lines of femur in a young adult. 
Posterior aspect. The lines of attachment of the articular 
capsules are in blue. 



THE PATELLA 



255 



A 

the most efficient manner in which stresses are transmitted is by the arrangement of the resist- 
mg material m Imes parallel to the direction in which the stresses occur and in the paths taken 
by the stresses. Theoretically the most efficient manner to attain these objects would be to pro- 
long the innermost filaments of the bone as straight lines parallel to the longitudinal axis of 
the bone, and gradually to flare the outer shell of compact bone outward, and continuing to give 
off filaments of bone parallel to the longitucUnal axis as the distal end of the femur is approached 
These filaments shoiUd be well-braced transversely and each should carry its proportionate 
part of the total load, parallel to the longitudinal axis, transmitting it eventually to the 
articular surface, and in a direction perpendicular to that surface." 

Referring to I^g. 249, it is seen that the large expansion of the bone is produced by the gradual 

transition of the hollow shaft of compact bone to cancellated bone, resulting in the production 

• of a much larger volume. The trabecule are given off from the shaft in lines parallel to the 

longitudinal axis, and are braced transversely by two series of trabecule at right angles to 

each other, in the same manner as required theoretically for economy. 

Although the action of the muscles exerts an appreciable effect on the stresses in the femur, 
it is relatively small and very complex to analyze and has not been considered in the aliove analysis! 

Ossification (Figs. 252, 253, 254).— The femur is ossified from five centers: one for the bodyj 
one for the head, one for each trochanter, and one for the lower extremity. Of all the long bones,' 
except the clavicle, it is the first to show traces of ossification ; this commences in the middle of 
the body, at about the seventh week of fetal life, and rapidly extends upward and downward. 
The centers in the epiphyses appear in the following order: in the lower end of the bone, at the 
ninth month of fetal Hfe (from this center the condyles and epicondyles are formed) ; in the head, 
at the end of the first year after birth; in the greater trochanter, during the fourth year; and 
in the lesser trochanter, between the thirteenth and fourteenth years. The order in which the 
epiphyses are joined to the body is the reverse of that of their appearance; they are not united 
until after puberty, the lesser trochanter being first joined, then the greater, then the head, and, 
lastly, the inferior extremity, which is not united until the twentieth year. 





Fig. 255. — Right patella. 
Anterior surface. 



Fig. 256.^Right patella. 
Posterior surface. 



The Patella (Knee Cap). 

The patella (Figs. 255, 256) is a flat, triangular bone, situated on the front of 
the knee-joint. It is usually regarded as a sesamoid bone, developed in the 
tendon of the Quadriceps femoris, 
and resembles these bones (1) in 
being developed in a tendon ; (2) in 
its center of ossification presenting 
a knotty or tuberculated outline; 
(3) in being composed mainly of 
dense cancellous tissue. It serves 
to protect the front of the joint, 
and increases the leverage of the 
Quadriceps femoris by making it 
act at a greater angle. It has an 
anterior and a posterior surface 
three borders, and an apex. 

Surfaces. — The anterior stirface is convex, perforated by small apertures for the 
passage of nutrient vessels, and marked by numerous rough, longitudinal stride. 
This surface is covered, in the recent state, by an expansion from the tendon of 
the Quadriceps femoris, which is continuous below with the superficial fibers of 
the ligamentum patella\ It is separated from the integument by a bursa. The 
posterior surface presents above a smooth, oval, articular area, di\ided into two 
facets by a vertical ridge; the ridge corresponds to the groove on the patellar 
surface of the femur, and the facets to the medial and lateral parts of the same 
surface; the lateral facet is the broader and deeper. Below the articular surface 
is a rough, convex, non-articular area, the lower half of which gives attachment 
to the ligamentum patellae; the upper half is separated from the head of the tibia 
by adipose tissue. 

Borders. — The base or superior border is thick, and sloped from behind, down- 
ward, and forward: it gives attachment to that portion of the Quadriceps femoris 



256 



OSTEOLOGY 



which is derived from the Rectus femoris and Vastus intermedius. The medial and 
lateral borders are thinner and converge below: they give attachment to those 
portions of the Quadriceps femoris which are derived from the Vasti lateralis and 

medialis. 

Apex. — The apex is pointed, and gives attachment to the ligamentum patelhe. 

Structure. — The patella consists of a nearly uniform dense cancellous tissue, covered by a 
thin compact lamina. The canceUi immediately beneath the anterior surface are arranged 
parallel with it. In the rest of the bone they radiate from the articular surface toward the other 
parts of the bone. 

Ossification. — The patella is ossified from a single center, which usually makes its appearance 
in the second or third year, but may be delayed until the sixth year. More rarely, the bone is 
developed by two centers, placed side by side. Ossification is completed about the age of puberty. 

Articulation. — The patella articulates with the femur. 




Inter condyloid eminence 

Fig. 257. — Upper surface of right tibia. 



The Tibia (Shin Bone). 

The tibia (Figs. 25S, 259) is situated at the medial side of the leg, and, 
excepting the femur, is the longest bone of the skeleton. It is prismoid in form, 

expanded above, where it enters into the 
Tuberosity knee-joint, contracted in the lower third, 

and again enlarged but to a lesser extent 
below. In the male, its direction is vertical, 
and parallel with the bone of the opposite 
side; but in the female it has a slightly 
oblique direction downward and lateralward, 
to compensate for the greater ol)liquity of 
the femur. It has a body and two extremities. 
The Upper Extremity {proximal extremity). 
— The upper extremity is large, and expanded 
into two eminences, the medial and lateral 
condyles. The superior articular surface pre- 
sents two smooth articular facets (Fig. 257). 
The medial facet, oval in shape, is slightly 
concave from side to side, and from before 
backward. The lateral, nearly circular, is 
concave from side to side, but slightly convex from before backward, especially 
at its posterior part, where it is prolonged on to the posterior surface for a 
short distance. The central portions of these facets articulate with the con- 
dyles of the femur, while their peripheral portions support the menisci of the 
knee-joint, which here intervene between the two bones. Between the artic- 
ular facets, but nearer the posterior than the anterior aspect of the l)one, is the 
intercondyloid eminence {spine of tibia), surmounted on either side by a prominent 
tubercle, on to the sides of which the articular facets are prolonged; in front of 
and behind the intercondyloid eminence are rough depressions for the attachment 
of the anterior and posterior cruciate ligaments and the menisci. The anterior 
surfaces of the condyles are continuous with one another, forming a large somewhat 
flattened area; this area is triangular, broad above, and perforated by large vascular 
foramina; narrow below where it ends in a large oblong elevation, the tuberosity of 
the tibia, which gives attachment to the ligamentum patellte; a bursa intervenes 
between the deep surface of the ligament and the part of the bone immediately 
above the tuberosity. Posteriorly, the condyles are separated from each other by 
a shallow depression, the posterior intercondyloid fossa, which gives attachment to 
part of the posterior cruciate ligament of the knee-joint. The medial condyle 
presents posteriorly a deep transverse groove, for the insertion of the tendon of 



THE TIBIA 



257 



the Semimembranosus. Its medial 
surface IS convex, rough, and promi- 
nent; it gives attachment to the 
tibial collateral ligament. The lat- 
eral condyle presents posteriorly a 
flat articular facet, nearly circular 
in form, directed downward, back- 
ward, and lateralward, for articu- 
lation with the head of the fibula. 
Its lateral surface is convex, rough, 
and prominent in front: on it is 
an eminence, situated on a level 
with the upper border of the tuber- 
osity and at the junction of its 
anterior and lateral surfaces, for 
the attachment of the iliotibial 
band. Just below this a part of 
the Extensor digitorum longus 
takes origin and a slip from the 
tendon of the Biceps femoris is 
inserted. 

The Body or Shaft {corjms tibia') . 
— The body has three borders and 
three surfaces. 

Borders. — The anterior crest or 
border, the most prominent of the 
three, commences above at the 
tuberosity, and ends below at the 
anterior margin of the medial 
malleolus. It is sinuous and 
prominent in the upper two-thirds 
of its extent, but smooth and 
rounded below; it gives attach- 
ment to the deep fascia of the leg. 

The medial border is smooth and 
rounded above and below, but 
more prominent in the center; it 
begins at the back part of the 
medial condyle, and ends at the 
posterior border of the medial 
malleolus; its uj^per part gives 
attachment to the tibial collat- 
eral ligament of the knee-joint 
to the extent of about 5 cm., 
and insertion to some fibers of 
the Popliteus; from its middle 
third some fibers of the Soleus 
and Flexor digitorum longus take 
origin. 

The interosseous crest or lateral 
border is thin and prominent, espe- 
cially its central part, and gives at- 
tachment to the interosseous mem- 
brane; it commences above in front 
of the fibular articular facet, and 
17 



Articular capsule 



.Vr^o'^-f/r,, 



-'"'Lr. 



■> (Ti/le 



J^eat 



Styloid process " 

Fibular 
collateral' 
ligament 






^^ 



01' 



i;,H:l""«»^tf^ 



i"iMv.:'»i/,„. 



J eVoji 



/ 



*V^ 



^^^. 



.igamemt/ 
Ipatell 



FIBULA liC ] 







'II 



Articular 
capsule 






Medial ■malleolus 

Lateral malleolus 
Fia. 258. — Bones of the right leg. Anterior surface. 



258 



OSTEOLOGY 



Articular 
cap; 



Articular 
capsule 

Styloid 
process 



FIBULA 



bifurcates below, to form the boundaries of a triangular rough surface, for the 
attachment of the interosseous ligament connecting the tibia and fibula. 

Surfaces. — The medial surface 
is smooth, convex, and broader 
above than below; its upper 
third, directed forward and 
medialward, is covered by the 
aponeurosis derived from the 
tendon of the Sartorius, and by 
the tendons of the Gracilis and 
Semitendinosus, all of which 
are inserted nearly as far for- 
ward as the anterior crest; in 
the rest of its extent it is sub- 
cutaneous. 

The lateral surface is narrower 
than the medial ; its upper two- 
thirds present a shallow groove 
for the origin of the Tibialis 
anterior; its lower third is 
smooth, convex, curves grad- 
ually forward to the anterior 
aspect of the bone, and is 
covered by the tendons of the 
Tibialis anterior. Extensor hal- 
lucis longus, and Extensor digi- 
torum longus, arranged in this 
order from the medial side. 

The posterior surface (Fig. 259) 
presents, at its upper part, a 
prominent ridge, the popliteal 
line, which extends obliquely 
downward from the back part of 
the articular facet for the fibula 
to the medial border, at the 
junction of its upper and middle 
thirds; it marks the lower limit 
of the insertion of the Popliteus, 
serves for the attachment of the 
fascia covering this muscle, and 
gives origin *to part of the 
Soleus, Flexor digitorum longus, 
and Tibialis posterior. The 
triangular area, above this line, 
gives insertion to the Popliteus. 
The middle third of the poste- 
rior surface is divided by a ver- 
tical ridge into two parts; the 
ridge begins at the popliteal line 
and is well-marked above, but 
indistinct below; the medial and 
broader portion gives origin to 
the Flexor digitorum longus, 
the lateral and narrower to part 
of the Tibialis posterior. The 




Articulates with talu^ 



Fia. 



Articula\r capsule 
259. — Bones of the right leg. Posterior surface. 



THE TIBIA 



259 



remaining part of the posterior surface is smooth and covered by the Tibialis 
posterior, Flexor digitorum longus, and Flexor hallucis longus. Immediately below 
the popliteal line is the nutrient foramen, which is large and directed oblicjuely 
downward. 

The Lower Extremity {distal extremity) .—The lower extremity, much smaller 
than the upper, presents five surfaces; it is prolonged downward on its medial 
side as a strong process, the medial malleolus. 

Surfaces. — The inferior articular surface is quadrilateral, and smooth for articu- 
lation with the talus. It is concave from before backward, broader in front than 
behind, and traversed from before backward by a slight elevation, separating 
two depressions. It is continuous with that on the medial malleolus. 



Upper extremily 



Appears before or 
shortly after birth 



Appears at 2nd , 

year 




Joins body 
about 20th year 




Joins body about 
\9.th year 



Lower extremity 




FlG. 260. — Plan of ossification of the tibia, 
centers. 



From three 



Fig. 



261. — Epiphysial lines of tibia and fibula 
in a young adult. Anterior aspect. 



The anterior surface of the lower extremity is smooth and rounded above, and 
covered by the tendons of the Extensor muscles ; its lower margin presents a rough 
transverse depression for the attachment of the articular capsule of the ankle- 
joint. 

The posterior surface is traversed by a shallow groove directed obliquely down- 
ward and medialward, continuous with a similar groove on the posterior surface 
of the talus and serving for the passage of the tendon of the Flexor hallucis longus. 

The lateral surface presents a triangular rough depression for the attachment 
of the inferior interosseous ligament connecting it with the fibula; the loMcr part 
of this depression is smooth, covered with cartilage in the fresh state, and articu- 
lates with the fibula. The surface is bounded by two prominent borders, con- 
tinuous above with the interosseous crest; they afford attachment to the anterior 
and posterior ligaments of the lateral malleolus. 

The medial surface is prolonged downward to form a strong pyramidal process, 
flattened from without inward — the medial malleolus. The medial surface of this 
process is convex and subcutaneous; its lateral or articular surface is smooth and 
slightly concave, and articulates with the talus; its anterior border is rough, for 



260 OSTEOLOGY 

the attachment of the anterior fibers of the deltoid Kgament of the ankle-joint; 
its 'posterior border presents a broad groove, the malleolar sulcus, directed obliquely 
downward and medialward, and occasionally double; this sulcus lodges the tendons 
of the Tibialis posterior and Flexor digitorum longus. The summit of the medial 
malleolus is marked by a rough depression behind, for the attachment of the 
deltoid ligament. 

Structure. — -The structure of the tibia is like that of the other long bones. The compact waU 
of the body is thickest at the junction of the middle and lower thirds of the bone. 

Ossification. — The tibia is ossified from three centers (Figs. 260, 2G1): one for the body and 
one for either extremity. Ossification begins in the center of the body, about the seventh week 
of fetal life, and gradually extends toward the extremities. The center for the upper epiphysis 
appears before or shortly after birth; it is flattened in form, and has a thin tongue-shaped process 
in front, which forms the tuberosity (Fig. 260) ; that for the lower epiphysis appears in the second 
year. The lower epiphj^sis joins the body at about the eighteenth, and the upper one joins about 
the twentieth year. Two additional centers occasionally exist, one for the tongue-shaped process 
of the upper epiphysis, which forms the tuberosity, and one for the medial malleolus. 

The Fibula (Calf Bone). 

The fibula (Figs. 258, 259) is placed on the lateral side of the tibia, with which 
it is connected above and below. It is the smaller of the two bones, and, in 
proportion to its length, the most slender of all the long bones. Its upper 
extremity is small, placed toward the back of the head of the tibia, below the level 
of the knee-joint, and excluded from the formation of this joint. Its lower extremity 
inclines a little forward, so as to be on a plane anterior to that of the upper end; 
it projects below the tibia, and forms the lateral part of the ankle-joint. The 
bone has a body and two extremities. 

The Upper Extremity or Head {capitulum fihid<E; proximal extremity). — The 
upper extremity is of an irregular quadrate form, presenting above a flattened 
articular surface, directed upward, forward, and medialward, for articulation with 
a corresponding surface on the lateral condyle of the tibia. On the lateral side 
is a thick and rough prominence continued behind into a pointed eminence, the 
apex {styloid process), which projects upward from the posterior part of the head. 
The prominence, at its upper and lateral part, gives attachment to the tendon of 
the Biceps femoris and to the fibular collateral ligament of the knee-joint, the liga- 
ment dividing the tendon into two parts. The remaining part of the circumference 
of the head is rough, for the attachment of muscles and ligaments. It presents in 
front a tubercle for the origin of the upper and anterior fibers of the Perona^us 
longus, and a surface for the attachment of the anterior ligament of the head; 
and behind, another tubercle, for the attachment of the posterior ligament of the 
head and the origin of the upper fibers of the Soleus. 

The Body or Shaft {corpus fihulce). — The body presents four borders — the 
antero-lateral, the antero-medial, the postero-lateral, and the postero-medial ; and 
four surfaces — anterior, posterior, medial, and lateral. 

Borders. — The antero-lateral border begins above in front of the head, runs ver- 
tically downward to a little below the middle of the bone, and then curving some- 
what lateralward, bifurcates so as to embrace a triangular subcutaneous surface 
immediately above the lateral malleolus. This border gives attachment to an 
intermuscular septum, which separates the Extensor muscles on the anterior 
surface of the leg from the Perona>i longus and brevis on the lateral surface. 

The antero-medial border, or interosseous crest, is situated close to the medial 
side of the preceding, and runs nearly parallel with it in the upper third of its 
extent, but diverges from it in the lower two-thirds. It begins above just beneath 
the head of the bone (sometimes it is quite indistinct for about 2.5 cm. below the 
head), and ends at the apex of a rough triangular surface immediately above the 



THE FIBULA 



261 



articular facet of the lateral malleolus. It serves for the attachment of the inter- 
osseous membrane, which separates the Extensor muscles in front from the Flexor 
muscles l)ehin(l. 

The postero-lateral border is prominent; it begins above at the apex, and ends 
below in the posterior border of the lateral malleolus. It is directed lateralward 
above, backward in the middle of its course, backward, and a little medialward 
below, and gives attachment to an aponeurosis which separates the Perona'i on 
the lateral surface from the Flexor muscles on the posterior surface. 

The postero-medial border, sometimes called the oblique line, begins above at the 
medial side of the head, and ends by becoming continuous with the interosseous 
crest at the lower fourth of the bone. It is well-marked and prominent at the upper 
and middle parts of the bone. It gives attachment to an aponeurosis which sep- 
arates the Tibialis posterior from the Soleus and Flexor hallucis longus. 



For talus 




Upper extremity 



Interosseous 
crest 



Appears about 
ith year 



Unites about 
25th year 



For posterior 
talofibular ligt. 



Appears at 
2nd' year 



Unites about 
20th year 



Lower extremity 



Fig. 262. — Lower extremity of right fibula. 
Medial aspect. 



Fig. 263. — Plan of ossification of the 
fibula. From three centers. 



Surfaces. — The anterior surface is the interval between the antero-lateral and 
antero-medial borders. It is extremely narrow and flat in the upper third of its 
extent; broader and grooved longitudinally in its lower third; it serves for the 
origin of three muscles: the Extensor digitorum longus. Extensor hallucis longus, 
and Peronjvus tertius. 

The posterior surface is the space included between the postero-lateral and the 
postero-medial borders; it is contiiuious below with the triangular area above 
the articular surface of the lateral malleolus; it is directed backward above, back- 
ward and medialward at its middle, directly medialward below. Its upper third 
is rough, for the origin of the Soleus; its lower part presents a triangular surface, 
connected to the tibia by a strong interosseous ligament; the intervening part of 
the surface is covered by the fibers of origin of the Flexor hallucis longus. Near 
the middle of this surface is the nutrient foramen, which is directed downward. 

The medial surface is the interval included between the antero-medial and the 
postero-medial borders. It is grooved for the origin of the Tibialis posterior. 



262 



OSTEOLOGY 



The lateral surface is the space between the antero-lateral and postero-lateral 
borders. It is broad, and often deeply grooved; it is directed lateralward in the 
upper two-thirds of its course, backward in the lower third, where it is continuous 
with the posterior border of the lateral malleolus. This surface gives origin to 
the Peronpei longus and brevis. 

The Lower Extremity or Lateral Malleolus {malleolus lateralis; distal extremity; 
external malleolus). — The lower extremity is of a pyramidal form, and somewhat 
flattened from side to side; it descends to a lower level than the medial malleolus. 
The lateral surface is convex, subcutaneous, and continuous with the triangular, 
subcutaneous surface on the lateral side of the body. The medial surface (Fig. 
262) presents in front a smooth triangular surface, convex from abo^•e downward, 
which articulates with a corresponding surface on the lateral side of the talus. 
Behind and beneath the articular surface is a rough depression, which gives attach- 
ment to the posterior talofibular ligament. The anterior border is thick and rough, 
and marked below by a depression for the attachment of the anterior talofibular 
ligament. The posterior border is broad and presents the shallow malleolar sulcus, 
for the passage of the tendons of the Perona?i longus and brevis. . The summit 
is rounded, and give attachment to the calcaneofibular ligament. 

Ossification. — The fibula is ossified from three centers (Fig. 263) : one for the body, and one 
for either end. Ossification begins in the body about the eighth week of fetal life, and extends 
toward the extremities. At birth the ends are cartilaginous. Ossification commences in the 
lower end in the second year, and in the upper about the fourth year. The lower epiphysis, 
the first to ossify, unites with the body about the twentieth year; the upper epiphysis joins 
about the twenty-fifth year. 

Groove for Peronoeus longus 



Trochlear process 

Middle articular surface 
Anterior artic. surface 

Post, artic. surface 




Trochlear process 

For cuboid bone 
For attachment 

of plantar calcaneo- 
cuboid ligament 

Sustentaculum 
tali 



Sustentaculum 
tali 

.j*[jff Sulcus calcanei 



Tuberosity 
Fig. 264. — Left calcaneus, superior surface. 




Sulcus for Flexor 
haUucis longus 



Medial process 

Tuberosity 

Lateral process 
Fig. 265. — Left calcaneus, inferior surface. 



THE FOOT. 

The skeleton of the foot (Figs. 268 and 269) consists of three parts: the tarsus, 
metatarsus, and phalanges. 



THE TARSUS 



263 



The Tarsus (Ossa Tarsi). 

The tarsal bones are seven in numl)er, viz., the calcaneus, talus, cuboid, navicular, 
and the first, second, and third cuneiforms. 

The Calcaneus (o5 calcis) (Figs. 264 to 267).— The calcaneus is the largest of the 
tarsal bones. It is situated at the lower and back part of the foot, serving to 
transmit the weight of the body to the ground, and forming a strong lever for 
the muscles of the calf. It is irregularly cuboidal in form, having its long axis 
directed forward and lateralward; it presents for examination six surfaces. 



Sulcus calcanei 
Middle articular surface for talus 



Posterior articular surface for talus 




Trochlear process 
Groove for Peronceus longus 



Lateral process 



Tuberosity 



Fig. 266. — Left calcaneus, lateral surface. 



Middle articular surface for talus 
. Sustentaculum tali 

Posterior articular surface for talus 



Tuberosity 





Anterior articular surface 
for talus 



Sulcus for Flexor 
hallucis longy^ 
Medial process 

Fig. 267. — Left calcaneus, medial surface. 



For cuboid bone 



Surfaces. — The superior surface extends behind on to that part of the bone which 
projects backward to form the heel. This varies in length in different individuals, 
is convex from side to side, concave from before backward, and supports a mass of 
fat placed in front of the tendo calcaneus. In front of this area is a large usually 
somewhat oval-shaped facet, the posterior articular surface, which looks upward 
and forward; it is convex from behind forward, and articulates with the posterior 
calcaneal facet on the under surface of the talus. It is bounded anteriorl}' by a 
deep depression w^hich is continued backward and medialward in the form of a 
groove, the calcaneal sulcus. In the articulated foot this sulcus lies below a similar 
one on the under surface of the talus, and the two form a canal (sinus tarsi) for the 



264 



OSTEOLOGY 



Groove J'or tendon of 
Peron^us longus 



Groove for tendon of 

PERON^fS BREVIS 



PERONiETJS TERTITTS 
PeRONjEUB BREVIS 




Groove for tendon of 
Flexor hallucis longus 



Tarsus 



Metatarsus 



-Ext. digitorcm bretis 



Phalanges 



Ext. hallccis longps 



Fig. 268. — Bonea of the right foot. Dorsal surface. 



THE TARSUS 



265 



Abductor hallucis 
Medial head of 



Lateral head of quadratus 

PLAKT^ 



Flexor hallccis brkvis 



Tubercle of 
naviczdar 



Tibialis anterior -( 



Two sesamoid 
bones 




Flexor brevis 
and abductor 

DIGITI t(UINTI 



Flexor digitorum 

BREVIS 



Flexor digitorum 

LONGUS 



Fig. 269. — Bones of the right foot. Plantar surface. 



266 OSTEOLOGY 

lodgement of the interosseous talocalcaneal ligament. In front and to the medial 
side of this groove is an elongated facet, concave from behind forward, and with its 
long axis directed forward and lateralward. This facet is frequently divided into 
two by a notch : of the two, the posterior, and larger is termed the middle articular 
surface; it is supported on a projecting process of bone, the sustentaculum tali, 
and articulates with the middle calcaneal facet on the under surface of the talus; 
the anterior articular surface is placed on the anterior part of the body, and articu- 
lates with the anterior calcaneal facet on the talus. The upper surface, anterior 
and lateral to the facets, is rough for the attachment of ligaments and for the origin 
of the Extensor digitorum brevis. 

The inferior or plantar surface is uneven, wider behind than in front, and con\ex 
from side to side; it is bounded posteriorly by a transverse elevation, the calcaneal 
tuberosity, which is depressed in the middle and prolonged at either end into a 
process; the lateral process, small, prominent, and rounded, gives origin to part 
of the Abductor digiti quinti; the medial process, broader and larger, gives attach- 
ment, by its prominent medial margin, to the Abductor hallucis, and in front 
to the Flexor digitorum brevis and the plantar aponeurosis; the depression between 
the processes gives origin to the Abductor digiti quinti. The rough surface in 
front of the processes gives attachment to the long plantar ligament, and to the 
lateral head of the Quadratus plantse; while to a prominent tubercle nearer the 
anterior part of this surface, as well as to a transverse groove in front of the tubercle, 
is attached the plantar calcaneocuboid ligament. 

The lateral surface is broad behind and narrow in front, flat and almost sub- 
cutaneous; near its center is a tubercle, for the attachment of the calcaneofibular 
ligament. At its upper and anterior part, this surface gives attachment to the 
lateral talocalcaneal ligament; and in front of the tubercle it presents a narrow 
surface marked by two oblique grooves. The grooves are separated by an elevated 
ridge, or tubercle, the trochlear process {^peroneal tubercle), which varies much in 
size in different bones. The superior groove transmits the tendon of the Peronaeus 
brevis; the inferior groove, that of the Peronseus longus. 

The medial surface is deeply' concave; it is directed obliquely downward and 
forward, and serves for the transmission of the plantar vessels and nerves into the 
sole of the foot; it affords origin to part -of the Quadratus plantae. At its upper 
and forepart is a horizontal eminence, the sustentaculum tali, which gives attach- 
ment to a slip of the tendon of the Tibialis posterior. This eminence is concave 
above, and articulates with the middle calcaneal articular surface of the talus; 
below, it is grooved for the tendon of the Flexor hallucis longus; its anterior margin 
gives attachment to the plantar calcaneonavicular ligament, and its medial, 
to a part of the deltoid ligament of the ankle-joint. 

The anterior or cuboid articular surface is of a somewhat triangular form. It is 
concave from above downward and lateralward, and convex in a direction at right 
angles to this. Its medial border gives attachment to the plantar calcaneonavicular 
ligament. 

The posterior surface is prominent, convex, wider below than above, and divisible 
into three areas. The lowest of these is rough, and covered by the fatty and fibrous 
tissue of the heel; the middle, also rough, gives insertion to the tendo calcaneus 
and Plantaris; while the highest is smooth, and is covered by a bursa which inter- 
venes between it and the tendo calcaneus. 

Articulations. — The calcaneus articulates with two bones: the talus and cuboid. 

The Talus {astragalus; ankle hone) (Figs. 270 to 273).— The talus is the second 
largest of the tarsal bones. It occupies the middle and upper part of the tarsus, 
supporting the tibia above, resting upon the calcaneus below, articulating on 
either side with the malleoli, and in front with the navicular. It consists of a 
body, a neck, and a head 



THE TARSUS 



267 



The Body (corpus tali).~The superior surface of the bodv presents, behind, a 
smooth trochlear surface, the trochlea, for articulation with the tihia. The trochlea 
is broader in front than behind, convex from before backward, slightlv concave 
from side to side: in front it is continuous with the upper surface of the neck of 
the bone. 



For medial malleolus 
Head 
Neck 



For lateral malleolu 
For inferior transverse ligament 




n 



Medial tubercle 
Sulcus for Flexor hallucis longus 



Trochlea, for tihia 
Lateral tubercle 

Fig. 270. — Left talus, from above. 



For plantar calcaneonavicular ligament 
For navicular bone 

Anterior calcaneal articular surface 



Sulcus tali 




^Posterior calcaneal articular 
surface 



Lateral tubercle 
Sulcus for Flexor hallucis longus 
Middle calcaneal articular surface 

Fig. 271. — Left talus, from below. 



The inferior surface presents two articular areas, the posterior and middle cal- 
caneal surfaces, separated from one another by a deep groove, the sulcus tali. 
The groove runs obliquely forward and lateralward, becoming gradually broader 
and deeper in front: in the articulated foot it lies above a similar groove upon 
the upper surface of the calcaneus, and forms, with it, a canal (sinus tarsi) filled 



268 



OSTEOLOGY 



up in the fresli state by the interosseous talocalcaneal ligament. The posterior 
calcaneal articular surface is large and of an oval or oblong form. It articulates 
with the corresponding facet on the upper surface of the calcaneus/ and is deeply 
concave in the direction of its long axis which runs forward and lateralward at 
an angle of about 45° with the median plane of the body. The middle calcaneal 
articular surface is small, oval in form and slightly convex; it articulates with the 
upper surface of the sustentaculum tali of the calcaneus. 

The medial surface presents at its upper part a pear-shaped articular facet for 
the medial malleolus, continuous above with the trochlea; below the articular 
surface is a rough depression for the attachment of the deep portion of the deltoid 
ligament of the ankle-joint. 



Trochlea for tibia 



Sulcus for Flex, hallucis longus 



For medial malleolus 



Neck 




For navicular bone 

For plantar calcaneonavicular ligament 
Fig. 272. — Left talus, medial surface. 



For lateral malleolus 




Sulcus tali 

Anterior calcaneal articular surface 
For navicular bone 

Fig. 273. — Left talus, lateral surface. 



Posterior calcaneal articular 
surface 



The lateral surface carries a large triangular facet, <3oncave from above downward, 
for articulation with the lateral malleolus; its anterior half is continuous above with 
the trochlea; and in front of it is a rough depression for the attachment of the ante- 
rior talofibular ligament. Between the posterior half of the lateral border of the 
trochlea and the posterior part of the base of the fibular articular surface is a tri- 
angular facet (Fawcett^) which comes into contact with the transverse inferior 
tibiofibular ligament during flexion of the ankle-joint; below the base of this facet 
is a groove which affords attachment to the posterior talofibular ligament. 

The posterior surface is narrow, and traversed by a groove running obliquely 

' Sewell (Journal of Anatomy and Physiology, vol. xxxviii) pointed out that in about 10 per cent, of bones a small 
triangular facet, continuous with the posterior calcaneal facet, is present at the junction of the lateral surface of the 
body with the posterior wall of the sulcus tali. 

2 Edinburgh Medical Journal, 1895. 



THE TARSUS 



269 



downward and medialward, and transmitting the tendoa of the Flexor hallucis 
longus. Lateral to the groove is a prominent tubercle, the posterior process, to 
which the posterior talofibular ligament is attached; this process is sometimes 
separated from the rest of the talus, and is then known as the os trigonum. Medial 
to the groove is a second smaller tubercle. 

The Neck (collum tali) .—The neck is directed forward and medialward, and 
comprises the constricted portion of the bone between the body and the oval head. 
Its upper and medial surfaces are rough, for the attachment of ligaments; its lateral 
surface is concave and is continuous below with the deep groove for the inter- 
osseous talocalcaneal ligament. 

The Head (cajyut tali). — The head looks forward and medialward; its anterior 
articular or navicular surface is large, oval, and convex. Its inferior surface has two 
facets, which are best seen in the fresh condition. The medial, situated in front 
of the middle calcaneal facet, is convex, triangular, or semi-oval in shape, and 
rests on the plantar calcaneonavicular ligament; the lateral, named the anterior 
calcaneal articular surface, is somewhat flattened, and articulates with the facet on 
the U])per surface of the anterior part of the calcaneus. 

Articulations. — The talus articulates with four bones: tibia, fibula, calcaneus, and navicular. 

The Cuboid Bone (os cuboideum) (Figs. 274, 275).— The cuboid bone is placed on 
the lateral side of the foot, in front of the calcaneus, and behind the fourth and fifth 
metatarsal bones. It is of a pyramidal shape, its base being directed medialward. 

For 3rd cuneiform For Ath metatarsal 



Occasional facet 
for navicular 



For 5th 
metatarsal 





Peronceal Tuberosity For calcaneus 
sulcus 



Fig. 274. — The left cuboid. Antero-medial view. 



Fig. 275. — The left cuboid. Postero-lateral view. 



Surfaces.^ — The dorsal surface, directed upward and lateralward, is rough, for the 
attachment of ligaments. The plantar surface presents in front a deep groove, 
the peroneal sulcus, which runs obliquely forward and medialward; it lodges the 
tendon of the Peronseus longus, and is bounded behind by a prominent ridge, 
to which the long plantar ligament is attached. The ridge ends laterally in an 
eminence, the tuberosity, the surface of which presents an oval facet; on this facet 
glides the sesamoid bone or cartilage frequently found in the tendon of the Pero- 
nseus longus. The surface of bone behind the groove is rough, for the attachment 
of the plantar calcaneocuboid ligament, a few fibers of the Flexor hallucis brevis, 
and a fasciculus from the tendon of the Tibialis posterior. The lateral surface 
presents a deep notch formed by the commencement of the peroneal sulcus. The 
posterior surface is smooth, triangular, and concavo-convex, for articulation with 
the anterior surface of the calcaneus; its infero-medial angle projects backward 
as a process which underlies and supports the anterior end of the calcaneus. The 
anterior surface, of smaller size, but also irregularly triangular, is divided by a 
vertical ridge into two facets: the medial, quadrilateral in form, articulates with 
the fourth metatarsal; the lateral, larger and more triangular, articulates with the 
fifth. The medial surface is broad, irregularly quadrilateral, and presents at 
its middle and upper part a smooth oval facet, for articulation with the third 



270 



OSTEOLOGY 



cuneiform; and behind this (occasionally) a smaller facet, for articulation with 
the navicular; it is rough in the rest of its extent, for the attachment of strong 
interosseous ligaments. 

Articulations. — The cuboid articulates with four bones: the calcaneus, third cuneiform, and 
fourth and fifth metatarsals; occasionally with a fifth, the navicular. 

The Navicular Bone {os naviculare pedis; scaphoid hone) (Figs. 276, 277). — The 
navicular bone is situated at the medial side of the tarsus, between the talus 
behind and the cuneiform bones in front. 



For 2nd cuneiform 



For 1st cuneiform 




For 3rd 
cuneiform 



Fig. 27G. — The left navicular. 



Occasional 
acet for 
cuboid 
Antero-lateral view. 



\^ 




For talus Tuberosity 
Fig. 277. — Theleft navicular. Postero-medialview. 



Surfaces. — The anterior surface is convex from side to side, and subdivided by two 
ridges into three facets, for articulation with the three cuneiform bones. The 
posterior surface is oval, concave, broader laterally than medially, and articulates 
with the rounded head of the talus. The dorsal surface is convex from side to side, 
and rough for the attachment of ligaments. The plantar surface is irregular, and 
also rough for the attachment of ligaments. The medial surface presents a rounded 

tuberosity, the lower part of which 
For 2nd For gives attachment to part of the 

For 1st metatarsal metatarsal 2nd cuneiform tendon of the Tibialis posterior. 

The lateral surface is rough and 
irregular for the attachment of 
ligaments, and occasionally pre- 
sents a small facet for articula- 
tion with the cuboid bone. 

Articulations. — Thenavicular articu- 
lates with four bones: the talus and 
the three cuneiforms; occasionally with 
a fifth, the cuboid. 





For tendon of 
Tibialis atiterior 



For Tvavicvlar 



Fig. 278.— The left fir.st cunei- 
form. Antero-niedial view. 



Fig. 279. — The left first cunei- 
form. Postero-lateral view. 



The First Cuneiform Bone {os 

cuneiform primum; intcrnalcunci- 

form) (Figs. 278, 279) .—The first 

cuneiform bone is the largest of 

the three cuneiforms. It is situated at the medial side of the foot, between the 

navicular behind and the base of the first metatarsal in front. 

Surfaces. — The medial surface is subcutaneous, broad, and quadrilateral; at its 
anterior plantar angle is a smooth oval impression, into which part of the tendon 
of the Tibialis anterior is inserted; in the rest of its extent it is rough for the 
attachment of ligaments. The lateral surface is concave, presenting, along its 
superior and posterior borders a narrow L-shaped surface, the vertical limb and 
posterior part of the horizontal limb of which articulate with the second cuneiform, 
while the anterior part of the horizontal limb articulates with the second metatarsal 



THE TARSUS 



271 



bone: the rest of this surface is rough for the attachment of ligaments and part 
of the tendon of the Peronjieus longus. The anterior surface, kidney-shaped and 
much larger than the posterior, articulates with the first metatarsal bone. The 
posterior surface is triangular, concave, and articulates with the most medial and 
largest of the three facets on the anterior surface of the navicular. The plantar 
surface is rough, and forms the base of the wedge; at its back part is a tuberosity 
for the insertion of part of the tendon of the Tibialis posterior. It also gives 
insertion in front to part of the tendon of the Tibialis anterior. The dorsal surface 
is the narrow end of the wedge, and is directed upward and lateralward; it is 
rough for the attachment of ligaments. 

Articulations. — The first cuneiform articulates with /our bones: the navicular, second cunei- 
form, and first and second metatarsals. 

The Second Cuneiform Bone {os cuneiforme secundum; middle cuneiform) (Figs. 
280, 281). — The second cuneiform bone, the smallest of the three, is of very reg- 
ular wedge-like form, the thin end being directed downward. It is situated between 
the other two cuneiforms, and articulates with the navicular behind, and the 
second metatarsal in front. 

Surfaces. — The anterior surface, triangular in form, and narrower than the pos- 
terior, articulates with the base of the second metatarsal bone. The posterior sur- 
face, also triangular, articulates with the intermediate facet on the anterior surface 
of the navicular. The medial surface carries an L-shaped articular facet, runnmg 
along the superior and posterior borders, for articulation with the first cuneiform, 
and is rough in the rest of its extent for the attachment of ligaments. The lateral 



For 1st cuneiform 



For navicular 





For 2nd metatarsal For Zrd cuneiform 



Fig. 280.- 
cuneiform, 
view. 



—The left second 
An t e r o-m e d i a 1 



Fig. 281. — The left 
second cuneiform. Pos- 
tero-lateral view. 



surface presents posteriorly a smooth 
facet for articulation with the third 
cuneiform bone. The dorsal surface 
forms the base of the wedge; it is 
quadrilateral and rough for the at- 
tachment of ligaments. The plantar 
surface, sharp and tuberculated, is 
also rough for the attachment of 
ligaments, and for the insertion of a 
slip from the tendon of the Tibialis 
posterior. 



Articulations. — The second cuneiform articulates with four bones: the navicular, first and 
third cuneiforms, and second metatarsal. 

The Third Cuneiform Bone {os cuneiforme tertium; external cuneiform) (Figs. 282, 
283). — -The third cuneiform bone, intermediate in size between the two preceding, 
is wedge-shaped, the base being uppermost. It occupies the center of the front row 
of the tarsal bones, between the second cuneiform medially, the cuboid laterally, 
the navicular behind, and the third metatarsal in front. 

Surfaces. — The anterior surface, triangular in form, articulates with the third 
metatarsal bone. The posterior surface articulates with the lateral facet on the 
anterior surface of the navicular, and is rough below for the attachment of liga- 
mentous fibers. The medial surface presents an anterior and a posterior articular 
facet, separated by a rough depression: the anterior, sometimes divided, articulates 
with the lateral side of the base of the second metatarsal bone ; the posterior skirts 
the posterior border, and articulates with the second cuneiform; the rough depres- 
sion gives attachment to an interosseous ligament. The lateral surface also pre- 
sents two articular facets, separated by a rough non-articular area; the anterior 
facet, situated at the superior angle of the bone, is small and semi-oval in shape, 
and articulates with the medial side of the base of the fourth metatarsal bone; 



272 



OSTEOLOGY 



the posterior and larger one is triangular or oval, and articulates with the cuboid; 
the rough, non-articular area serves for the attachment of an interosseous ligament. 
The three facets for articulation with the three metatarsal bones are continuous 
with one another; those for articulation with the second cuneiform and na\icular 
are also continuous, but that for articulation with the cuboid is usually separate. 
The dorsal surface is of an oblong form, its postero-lateral angle being prolonged 
backward. The plantar sixrface is a rounded margin, and serves for the attachment 
of part of the tendon of the Tibialis posterior, part of the Flexor hallucis brevis, 
and ligaments. 

Articulations. — The third cuneiform articulates with six bones: the navicular, second cunei- 
form, cuboid, and second, third, and fourth metatarsals. 



For navicular For 2nd cuneiform 




Fig. 2S2.- 



-The left third cuneiform. 
\"iew. 



For 2nd 
metatarsal 



Postero-medial 



For ith 
tnclaiarsal 



For cuboid 




Fig. 



ForZrd 
metatarsal 

283. — The third left cuneiform, 
lateral view. 



Antero- 



The Metatarsus. 

The metatarsus consists of five bones which are numbered from the medial 
side {ossa metatarsalia I.-V.); each presents for examination a body and two 
extremities. 

Common Characteristics of the Metatarsal Bones. — The body is prismoid in 
form, tapers gradually from the tarsal to the phalangeal extremity, and is curved 
longitudinally, so as to be concave below, slightly convex above. The base or 
posterior extremity is wedge-shaped, articulating proximally with the tarsal bones, 
and by its sides with the contiguous metatarsal bones: its dorsal and plantar 
surfaces are rough for the attachment of ligaments. The head or anterior extremity 
presents a convex articular surface, oblong from above downward, and extend- 
ing farther backward below than above. Its sides are flattened, and on each is a 
depression, surmounted by a tubercle, for ligamentous attachment. Its plantar 
surface is grooved antero-posteriorly for the passage of the Flexor tendons, and 
marked on either side bv an articular eminence continuous with the terminal 
articular surface. 

Characteristics of the Individual Metatarsal Bones. — The First Metatarsal 
Bone {os metatarsale I; metatarsal bone of the great toe) (Fig. 284). — The first 
metatarsal bone is remarkable for its great thickness, and is the shortest of 
the metatarsal bones. The body is strong, and of well-marked prismoid form. 
The base presents, as a rule, no articular facets on its sides, but occasionally 
on tlie lateral side there is an oval facet, by which it articulates with the second 
metatarsal. Its proximal articular surface is of large size and kidney-shaped; its 
circumference is grooved, for the tarsometatarsal ligaments, and medially gives 
insertion to part of the tendon of the Tibialis anterior; its plantar angle presents 
a rough oval prominence for the insertion of the tendon of the Peronieus longus. 
The head is large; on its plantar surface are two grooved facets, on which glide 
sesamoid bones; the facets are separated by a smooth elevation. 



THE METATARSUS 



273 



The Second Metatarsal Bone {os metatarsale II) (Fig. 285).— The second meta- 
tarsal bone is the longest of the metatarsal bones, being prolonged backward 

For sesamoid bones 




For 1st For Peroncsus 

cuneiform longus 

Fig. 284. — The first metatarsal. (Left.) 




For 3rd 

metatarsal 




For 1st 

cuneiform For 2nd For Hnl 

cuneiform cuneiform 

FiQ. 285. — The second metatarsal. (Left.) 




F(yr 2nd 
metatarsal 

For 

Brd 
cuneiform 

Fig. 286. — The third metatarsal. (Left.) 



'or 2tld 
meta- 
tarsal 



For Uh 
metatarsal 




For 3ra 
metatarsal 




For cuboid J 

Far %rd cuneiform For 5th metatarsal 

Fig. 287. — The fourth metatarsal. (Left.) 



into the recess formed by the three cuneiform bones. Its base is broad above, 
narrow and rough below. It presents four articular surfaces: one behind, of a 
triangular form, for articulation with the second cuneiform; one at the upper part 
18 



274 



OSTEOLOGY 



of its medial surface, for articulation with the first cuneiform ; and two on its lateral 
surface, an upper and lower, separated by a rough non-articular interval. Each 
of these lateral articular surfaces is divided into two by a vertical ridge; the two 
anterior facets articulate with the third metatarsal; the two posterior (sometimes 
continuous) with the third cuneiform. A fifth facet is occasionally present for 
articulation with the first metatarsal; it is oval in shape, and is situated on the 
medial side of the body near the base. 

The Third Metatarsal Bone {os metatarsale III) (Fig. 286). — The third meta- 
tarsal bone articulates proximally, by means of a triangular smooth surface, 
with the third cuneiform; medially, by two facets, with the second metatarsal; 
and laterally, by a single facet, with the fourth metatarsal. This last facet is 
situated at the dorsal angle of the base. 



;n 



For 4:th 
metatarsal For cuboid Tvberosity 

Fig. 288.— The fifth metatarsal. (Left.) 

The Fourth Metatarsal Bone {os metatarsale IV) (Fig. 287). — The fourth meta- 
tarsal bone is smaller in size than the preceding; its base presents an oblique 
quadrilateral surface for articulation with the cuboid ; a smooth facet on the medial 
side, divided by a ridge into an anterior portion for articulation with the third 
metatarsal, and a posterior portion for articulation with the third cuneiform; on 
the lateral side a single facet, for articulation with the fifth metatarsal. 

The Fifth Metatarsal Bone {os metatarsale V) (Fig. 288).— The fifth metatarsal 
bone is recognized by a rough eminence, the tuberosity, on the lateral side of its 
base. The base articulates behind, by a triangular surface cut obliquely in a trans- 
verse direction, with the cuboid; and medially, with the fourth metatarsal. On 
the medial part of its dorsal surface is inserted the tendon of the Peronseus tertius 
and on the dorsal surface of the tuberosity that of the Peronaeus brevis. A strong 
band of the plantar aponeurosis connects the projecting part of the tuberosity 
with the lateral process of the tuberosity of the calcaneus. The plantar surface 
of the base is grooved for the tendon of the Abductor digiti quinti, and gives origin 
to the Flexor digiti quinti brevis. 

Articulations. — The base of each metatarsal bone articulates with one or more of the tarsal 
bones, and the head with one of the first row of phalanges. The first metatarsal articulates with 
the first cuneiform, the second with all three cuneiforms, the third with the third cuneiform, the 
fourth with the third cuneiform and the cuboid, and the fifth with the cuboid. 



THE PHALANGES OF THE FOOT 



275 



The Phalanges of the Foot (Phalanges Digitorum Pedis). 

The phalanges of the foot correspond, in number and general arrangement, 
with those of the hand; there are two in the great toe, and three in each of the 
other toes. They differ from them, however, in their size, the bodies being much 
reduced in length, and, especially in the first row, laterally compressed. 

First Row. — The body of each is compressed from side to side, convex above, 
concave below. The base is concave; and the head presents a trochlear surface 
for articulation with the second phalanx. 

Second Row. — The phalanges of the second row are remarkably small and short, 
but rather broader than those of the first row. 

The ungual phalanges, in form, resemble those of the fingers; but they are smaller 
and are flattened from above downward; each presents a broad base for articula- 
tion with the corresponding bone of the second row, and an expanded distal 
extremity for the support of the nail and end of the toe. 






TARSUS. 

One center for each bone, 
except calcaneus 



OUTER FOUR METATARSALS. 

Tv)o centers for each bone . 
One for body 
One for head 



PHALANGES. 



Two centers for each bone : 
One for body 
One for metatarsal 
extremity 




Appears 10th year; 
unites after puberty 



Appears 3rd year 
Unite I8th-20th year 

Appears 7th week 



Apps. Ith wk. — 



Unite 18-20 yr. | m 
Apps. 3rd yr. 



App. 4th yr 
Unite 17-18 yr. > 



^S) 



f:::^* 



App. 2-4 mo. — ' 





App. 6-7th yr. . 
Unite 17-18 rjr. I \ 

App. 2-4 »no. 

App. 6th yr. ^ 
Unite 17-18 yr. ] I 

App. 7th wk. — W|: 

CD 

Fig. 289. — Plan of ossification of the foot. 

Articulations.— In the second, third, fourth, and fifth toes the phalanges of the first row articu- 
late behind with the metatarsal bones, and in front with the second phalanges, which in their 
turn articulate with the first and third: the ungual phalanges articulate with the second. 

Ossification of the Bones of the Foot (Fig. 289).— The tarsal bones are each ossified from a 
dngle center, excepting the calcaneus, which has an epiphysis for its posterior extremity, ihe 
centers make their appearance in the following order: calcaneus at the sixth month ot tetal lile, 



276 OSTEOLOGY 

talus, about the seventh month; cuboid, at the ninth month; third cuneiform, during the first 
year; first cuneiform, in the third year; second cuneiform and navicular, in the fourth year. 
The epiphysis for the posterior extremity of the calcaneus appears at the tenth year, and unites 
with the rest of the bone soon after puberty. The posterior process of the talus is sometimes 
ossified from a separate center, and may remain distinct from the main mass of the bone, when 
it is named the os trigonum. 

The metatarsal bones are each ossified from Iwo centers: one for the body, and one for the 
head, of the second, third, fourth, and fifth metatarsals; one for the body, and one for the base, 
of the first metatarsal.^ Ossification commences in the center of the body about the ninth week, 
and extends toward either extremity. The center for the base of the first metatarsal appears 
about the third year; the centers for the heads of the other bones between the fifth and eighth 
years; they join the bodies between the eighteenth and twentieth years. 

The phalanges are each ossified from two centers: one for the body, and one for the base. 
The center for the body appears about the tenth week, that for the base between the fourth and 
tenth years; it joins the body about the eighteenth year. 

Comparison of the Bones of the Hand and Foot. 

The hand and foot are constructed on somewhat similar principles, each con- 
sisting of a proximal part, the carpus or the tarsus, a middle portion, the meta- 
carpus, or the metatarsus, and a terminal portion, the phalanges. The proximal 
part consists of a series of more or less cubical bones which allow a slight amount 
of gliding on one another and are chiefly concerned in distributing forces transmitted 
to or from the bones of the arm or leg. The middle part is made up of slightly 
movable long bones which assist the carpus or tarsus in distributing forces and 
also give greater breadth for the reception of such forces. The separation of the 
individual bones from one another allows of the attachments of the Interossei and 
protects the dorsi-palmar and dorsi-plantar vascular anastomoses. The terminal 
portion is the most movable, and its separate elements enjoy a varied range of 
movements, the chief of which are flexion and extension. 




Fig. 290. — Skeleton of foot. Medial aspect. 

The function of the hand and foot are, however, very different, and the general 
similarity between them is greatly modified to meet these requirements. Thus the 
foot forms a firm basis of support for the body in the erect posture, and is there- 
fore more solidly built up and its component parts are less movable on each other 
than those of the hand. In the case of the phalanges the difference is readily 
noticeable; those of the foot are smaller and their movements are more limited 
than those of the hand. Very much more marked is the difference between the 
metacarpal bone of the thumb and the metatarsal bone of the great toe. The meta- 
carpal bone of the thumb is constructed to permit of great mobility, is directed at 
an acute angle from that of the index finger, and is capable of a considerable range 

1 As was noted in the first metacarpal (see footnote, page 231), so in the first metatarsal, there is often a second 
epiphysis for its head. 



THE SESAMOID BONES 



277 



of movements at its articulation with the carpus. The metatarsal bone of the 
great toe assists in supporting the weight of the body, is constructed with great 
solidity, lies parallel with the other metatarsals, and has a very limited degree of 
mobility. The carpus is small in proportion to the rest of the hand, is placed 
in line with the forearm, and forms a transverse arch, the concavity of which 
constitutes a bed for the Flexor tendons and the palmar vessels and nerves. The 
tarsus forms a considerable part of the foot, and is placed at right angles to the 
leg, a position which is almost peculiar to man, and has relation to his erect pos- 
ture. In order to allow of their supporting the weight of the body with the least 
expenditure of material the tarsus and a part of the metatarsus are constructed 
in a series of arches (Figs. 290, 291), the disposition of which will be considered 
after the articulations of the foot have been described. 




Fig. 291. — Skeleton of foot. Lateral aspect. 



The Sesamoid Bones (Ossa Sesamoidea). 

Sesamoid bones are small more or less rounded masses embedded in certain 
tendons and usually related to joint surfaces. Their functions probably are to 
modify pressure, to diminish friction, and occasionally to alter the direction of a 
muscle pull. That they are not developed to meet certain physical requirements 
in the adult is evidenced by the fact that they are present as cartilaginous nodules 
in the fetus, and in greater numbers than in the adult. They must be regarded, 
according to Thilenius, as integral parts of the skeleton phylogenetically inherited.^ 
Physical necessities probably come into play in selecting and in regulating the 
degree of development of the original cartilaginous nodules. Nevertheless, irreg- 
ular nodules of bone may appear as the result of intermittent pressure in certain 
regions, e. g., the "rider's bone," which is occasionally developed in the Adductor 
muscles of the thigh. 

Sesamoid bones are invested by the fibrous tissue of the tendons, except on the 
surfaces in contact with the parts over which they glide, where they present 
smooth articular facets. 

In the upper extremity the sesamoid bones of the joints are found only on the 
palmar surface of the hand. Two, of which the medial is the the larger, are constant 
at the metacarpophalangeal joint of the thumb; one is frequently present in the 
corresponding joint of the little finger, and one (or two) in the same joint of the 
index finger. Sesamoid bones are also found occasionally at the metacarpopha- 
langeal joints of the middle and ring fingers, at the interphalangeal joint of the 
thumb and at the distal interphalangeal joint of the index finger. 

In the lower extremity the largest sesamoid bone of the joints is the patella, 
developed in the tendon of the Quadriceps femoris. On the plantar aspect of the 
foot, two, of which the medial is the larger, are always present at the metatar- 

> Morpholog. Arbeiten, 1906, v, 309. 



278 OSTEOLOGY 

sophalangeal joint of the great toe; one sometimes at the metatarsophalangeal 
joints of the second and fifth toes, one occasionally at the corresponding joint of 
the third and fourth toes, and one at the interphalangeal joint of the great toe. 

Sesamoid bones apart from joints are seldom found in the tendons of the upper 
limb; one is sometimes seen in the tendon of the Biceps brachii opposite the radial 
tuberosity. They are, however, present in several of the tendons of the lower 
limb, viz., one in the tendon of the Peronseus longus, where it glides on the cuboid; 
one, appearing late in life, in the tendon of the Tibialis anterior, opposite the smooth 
facet of the first cuneiform bone ; one in the tendon of the Tibialis posterior, oppo- 
site the medial side of the head of the talus; one in the lateral head of the Gastroc- 
nemius, behind the lateral condyle of the femur; and one in the tendon of the Psoas 
major, where it glides over the pubis. Sesamoid bones are found occasionally 
in the tendon of the Glutaeus maximus, as it passes over the greater trochanter, 
and in the tendons which wind around the medial and lateral malleoli. 



SYNDESMOLOGY. 



rjIHE bones of the skeleton are joined to one another at different parts of their 
J- surfaces, and such connections are termed Joints or Articulations. ^Yhe^e 
the joints are immomble, as in the articulations between practically all the bones 
of the skull, the adjacent margins of the bones are almost in contact, being separated 
merely by a thin layer of fibrous membrane, named the sutural ligament. In certain 
regions at the base of the skull this fibrous membrane is replaced by a layer of car- 
tilage. ^Yhe^e sligJit movement combined with great strength is required, the osseous 
surfaces are united by tough and elastic fibrocartilages, as in the joints between the 
vertebral bodies, and in the interpubic articulation. In the freely movable joints 
the surfaces are completely separated; the bones forming the articulation are ex- 
panded for greater convenience of mutual connection, covered by cartilage and 
enveloped by capsules of fibrous tissue. The cells lining the interior of the fibrous 
capsule form an imperfect membrane — the synovial membrane — which secretes 
a lubricating fluid. The joints are strengthened by strong fibrous bands called 
ligaments, which extend betw^een the bones forming the joint. 

Bone. — Bone constitutes the fundamental element of all the joints. In the 
long bones, the extremities are the parts which form the articulations; they are 
generally somewhat enlarged; and consist of spongy cancellous tissue with a thin 
coating of compact substance. In the flat bones, the articulations usually take 
place at the edges; and in the short bones at various parts of their surfaces. The 
layer of compact bone which forms the joint surface, and to which the articular 
cartilage is attached, is called the articular lamella. It differs from ordinary 
bone tissue in that it contains no Haversian canals, and its lacunae are larger 
and have no canaliculi. The vessels of the cancellous tissue, as they approach 
the articular lamella, turn back in loops, and do not perforate it; this layer is con- 
sequently denser and firmer than ordinary bone, and is evidently designed to form 
an unyielding support for the articular cartilage. 

Cartilage. — Cartilage is a non-vascular structure which is found in various 
parts of the body — in adult life chiefly in the joints, in the parietes of the thorax, 
and in various tubes, such as the trachea and bronchi, nose, and ears, which require 
to be kept permanently open. In the fetus, at an early period, the greater part 
of the skeleton is cartilaginous; as this cartilage is afterward replaced by bone, 
it is called temporary, in contradistinction to that which remains unossified during 
the whole of life, and is called permanent. 

Cartilage is divided, according to its minute structure, into hyaline cartilage, 
white fibrocartilage, and yellow or elastic fibrocartilage. 

Hyaline Cartilage. — Hyaline cartilage consists of a gristly mass of a firm consist- 
ence, but of considerable elasticity and pearly bluish color. Except where it coats 
the articular ends of bones, it is covered externally by a fibrous membrane, the 
perichondrium, from the vessels of which it imbibes its nutritive fluids, being itself 
destitute of bloodvessels. It contains no nerves. Its intimate structure is very 
simple. If a thin slice be examined under the microscope, it will be found to consist 
of cells of a rounded or bluntly angular form, lying in groups of two or more in 
a granular or almost homogeneous matrix (Fig. 292). The cells, when arranged 
in groups of two or more, have generallv straight outlines where they are in contact 

(279) 



280 



SYNDESMOLOGY 



with each other, and in the rest of their circumference are rounded. They con- 
sist of clear translucent protoplasm in which fine interlacing filaments and minute 
granules are sometimes present; imbedded in this are one or two round nuclei, 
having the usual intranuclear network. The cells are contained in cavities in 
the matrix, called cartilage lacunae; around these the matrix is arranged in con- 
centric lines, as if it had been formed in successive portions around the cartilage 
cells. This constitutes the so-called capsule of the space. Each lacuna is generally 

occupied by a single cell, but dur- 
ing the division of the cells it may 
contain two, four, or eight cells. 

The matrix is transparent and 
apparently without structure, or 
else presents a dimly granular ap- 
pearance, like ground glass. Some 
observers ha\'e shown that the 
matrix of hyaline cartilage, and 
especially of the articular variety, 
after prolonged maceration, can 
be broken up into fine fibrils. 
These fibrils are probably of the same nature, chemically, as the white fibers 
of connective tissue. It is believed by some histologists that the matrix is per- 
meated by a number of fine channels, which connect the lacunae with each other, 
and that these canals communicate with the lymphatics of the perichondrium, 
and thus' the structure is permeated by a current of nutrient fluid. 

Articular cartilage, costal cartilage, and temporary cartilage are all of the hyaline 
variety. They present dift'erences in the size, shape, and arrangement of their 
cells. 




Fig. 292. — Human cartilage cells from the cricoid cartilage. 

X 350 




I Superficial flattened cells 



^^^^^t 'ffsvQl \ Vertical rows of cells 



' Calcified matrix 



Jr- BoTie 
Fig. 293. — Vertical section of articular cartilage. 




Fig. 294. — Costal cartilage from a man, aged 
seventy-six years, showing the development of 
fibrous structure in the matrix. In several por- 
tions of the specimen two or three generations of 
cells are seen enclosed in a parent cell wall. 
Highly magnified. 



In Articular Cartilage (Fig. 293), which shows no tendency to ossification, the 
matrix is finely granular; the cells and nuclei are small, and are disposed parallel 
to the surface in the superficial part, while nearer to the bone they are arranged in 
vertical rows. Articular cartilages have a tendency to split in a vertical direction ; 
in disease this tendency becomes very manifest. The free surface of articular 
cartilage, where it is exposed to friction, is not covered by perichondrium, although 
a layer of connective tissue continuous with that of the synovial membrane can be 



CARTILAGE 



281 



traced iu the adult over a small part of its circumference, and here the cartilage 
cells are more or less branched and pass insensibly into the branched connective 
tissue corpuscles of the synovial membrane. Articular cartilage forms a thin 
incrustation upon the joint surfaces of the bones, and its elasticity enables it to 
break the force of concussions, while its smoothness affords ease and freedom of 
movement. It varies in thickness according to the shape of the articular surface 
on which it lies; where this is convex the cartilage is thickest at the center, the 
reverse being the case on concave articular surfaces. It appears to derive its 
nutriment partly from the vessels of the neighboring synovial membrane and 
partly from those of the bone upon which it is implanted. Toynbee has shown 
that the minute vessels of the cancellous tissue as they approach the articular 
lamella dilate and form arches, and then return into the substance of the bone. 

In Costal Cartilage the cells and nuclei are large, and the matrix has a tendency 
to fibrous striation, especially in old age (Fig. 294). In the thickest parts of the 
costal cartilages a few large vascular channels may be detected. This appears, 
at first sight, to be an exception to the statement that cartilage is a non-vascular 
tissue, but is not so really, for the vessels give no branches to the cartilage sub- 
stance itself, and the channels may rather be looked upon as involutions of the 
perichondrium. The xiphoid process and the cartilages of the nose, larynx, and 
trachea (except the epiglottis and corniculate cartilages of the larynx, which are 
composed of elastic fibrocartilage) resemble the costal cartilages in microscopic 
characteristics. The arvtenoid cartilage of the larvnx shows a transition from 
hyaline cartilage at its base to elastic cartilage at the apex. 

The hyaline cartilages, especially in adult and advanced life, are prone to calcify 
— that is to say, to have their matrix permeated by calcium salts without any 
appearance of true bone. The process of calcification occurs frequently, in such 
cartilages as those of the trachea and in the costal cartilages, where it may be 
succeeded by conversion into true bone. 

White Fibrocartilage. — White fibrocartilage consists of a mixture of white fibrous 
tissue and cartilaginous tissue in various proportions; to the former of these con- 
stituents it owes its flexibility and 
toughness, and to the latter its 
elasticity. When examined under 
the microscope it is found to be 
made up of fibrous connective 
tissue arranged in bundles, with 
cartilage cells between the bundles; 
the cells to a certain extent re- 
semble tendon cells, but may be 
distinguished from them by being 
surrounded by a concentrically 
striated area of cartilage matrix 
and by being less flattened (Fig. 
295) . The white fibrocartilages ad- 
mit of arrangement into four 
groups — interarticular, connecting, 
circumferential, and stratiform. , 

1. The Interarticular Fibrocartilages {menisci) are flattened fibrocartilagmous 
plates, of a round, oval, triangular, or sickle-like form, interposed between the 
articular cartilages of certain joints. They are free on both surfaces, usually 
thinner toward the center than at the circumference, and held m position by the 
attachment of their margins and extremities to the surrounding ligaments, ihe 
synovial membranes of the joints are prolonged over them. They are found 
in the temporomandibular, sternoclavicular, acromioclavicular, wrist, and knee 




Fig. 29o. — White fibrocartilage from an intervertebral 
fibrocartilage. 



282 SYNDESMOLOGY 

joints — i. e., in those joints which are most exposed to violent concussion and 
subject to frequent movement. Their uses are to obHterate the intervals between 
opposed surfaces in their various motions; to increase the depths of the articular 
surfaces and give ease to the gliding movements; to moderate the effects of great 
pressure and deaden the intensity of the shocks to which the parts may be sub- 
jected. Humphry has pointed out that these interarticular fibrocartilages serve 
an important purpose in increasing the varieties of movement in a joint. Thus 
in the knee joint there are two kinds of motion, viz., angular movement and rota- 
tion, although it is a hinge joint, in which, as a rule, only one variety of motion 
is permitted; the former movement takes place between the condyles of the femur 
and the interarticular cartilages, the latter between the cartilages and the head 
of the tibia. So, also, in the temporomandibular joint, the movements of opening 
and shutting the mouth take place between the fibrocartilage and the mandible, 
the grinding movement between the mandibular fossa and the fibrocartilage, the 
latter moving with the mandible. 

2. The Connecting Fibrocartilages are interposed between the bony surfaces of 
those joints which admit of only slight mobility, as between the bodies of the 
vertebrae. They form disks which are closely adherent to the opposed surfaces. 
Each disk is composed of concentric rings of fibrous tissue, 'with cartilaginous 
laminae interposed, the former tissue predominating toward the circumference, 
the latter toward the center. 

3. The Circumferential Fibrocartilages consist of rims of fibrocartilage, which 
surround the margins of some of the articular cavities, e. g., the glenoidal labrum 
of the hip, and of the shoulder; they serve to deepen the articular cavities and to 
protect their edges. 

4. The Stratiform Fibrocartilages are those which form a thin coating to osseous 
grooves through which the tendons of certain muscles glide. Small masses of fibro- 
cartilage are also developed in the tendons of some muscles, where they glide 
over bones, as in the tendons of the Perona^us longus and Tibialis posterior. 

The distinguishing feature of cartilage chemically is that it yields on boiling a 
substance called chondrin, very similar to gelatin, but differing from it in several 
of its reactions. It is now believed that chondrin is not a simple body, but a 
mixture of gelatin with mucinoid substances, chief among which, perhaps, is a 
compound termed chondro-mucoid. 

Ligaments. — Ligaments are composed mainly of bundles of white fibrous tissue 
placed parallel with, or closely interlaced with one another, and present a white, 
shining, silvery appearance. They are pliant and flexible, so as to allow perfect 
freedom of movement, but strong, tough, and inextensible, so as not to yield 
readily to applied force. Some ligaments consist entirely of yellow elastic tissue, 
as the ligamenta flava which connect together the laminae of adjacent vertebrae, 
and the ligamentum nuchae in the lower animals. In these cases the elasticity of 
the ligament is intended to act as a substitute for muscular power. 

The Articular Capsules. — The articular capsules form complete envelopes for the 
freely movable joints. Each capsule consists of two strata — an external {stratum 
fibrosum) composed of white fibrous tissue, and an internal (stratum synoviale) 
which is a secreting layer, and is usually described separately as the synovial 
membrane. 

The fibrous capsule is attached to the whole circumference of the articular end 
of each bone entering into the joint, and thus entirely surrounds the articulation. 

The synovial membrane invests the inner surface of the fibrous capsule, and is 
reflected over any tendons passing through the joint cavity, as the tendon of the 
Popliteus in the knee, and the tendon of the Biceps brachii in the shoulder. It is 
composed of a thin, delicate, connective tissue, with branched connective-tissue 
corpuscles. Its secretion is thick, viscid, and glairy, like the white of an egg, and 



DEVELOPMENT OF THE JOINTS 283 

is hence termed synovia. In the fetus this membrane is said, by Toynbee, to be 
continued over the surfaces of the cartilages; but in the adult such a continuation 
is wanting, excepting at the circumference of the cartilage, upon which it encroaches 
for a short distance and to which it is firmly attached! In some of the joints the 
synovial membrane is thrown into folds which pass across the cavity; they are 
especially distinct in the knee. In other joints there are flattened folds, subdivided 
at their margins into fringe-like processes which contain convoluted vessels. 
These folds generally project from the synovial membrane near the margin of the 
cartilage, and lie flat upon its surface. They consist of connective tissue, covered 
with endothelium, and contain fat cells in variable quantities, and, more rarely, 
isolated cartilage cells; the larger folds often contain considerable quantities of fat. 

Closely associated with synovial membrane, and therefore conveniently described 
in this section, are the mucous sheaths of tendons and the mucous bursoe. 

Mucous sheaths (vagina; mucosos) serve to facilitate the gliding of tendons in 
fibroosseous canals. Each sheath is arranged in the form of an elongated closed 
sac, one layer of which adheres to the wall of the canal, and the other is reflected 
upon the surface of the enclosed tendon. These sheaths are chiefly found surround- 
ing the tendons of the Flexor and Extensor muscles of the fingers and toes as they 
pass through fibroosseous canals in or near the hand and foot. 

Bursse mucosae are interposed between surfaces which glide upon each other. 
They consist of closed sacs containing a minute quantity of clear viscid fluid, and 
may be grouped, according to their situations, under the headings subcutaneous, 
submuscular, subfacial, and subtendinous. 

DEVELOPMENT OF THE JOINTS. 

The mesoderm from which the different parts of the skeleton are formed shows 
at first no dilTerentiation into masses corresponding with the individual bones. 
Thus continuous cores of mesoderm form the axes of the limb-buds and a continu- 
ous column of mesoderm the future vertebral column. The first indications of the 
bones and joints are circumscribed condensations of the mesoderm; these condensed 
parts become chondrified and finally ossified to form the bones of the skeleton. 
The intervening non-condensed portions consist at first of undift'erentiated meso- 
derm, which may develop in one of three directions. It may be converted into 
fibrous tissue as in the case of the skull bones, a synarthrodial joint being the 
result, or it may become partly cartilaginous, in which case an amphiarthrodial 
joint is formed. Again, it may become looser in texture and a cavity ultimately 
appear in its midst; the cells lining the sides of this cavity form a synovial mem- 
brane and thus a diarthrodial joint is developed. 

The tissue surrounding the original mesodermal core forms fibrous sheaths for 
the developing bones, /. c., periosteum and perichondrium, which are continued 
between the ends of the bones over the synovial membrane as the capsules of the 
joints. These capsules are not of uniform thickness, so that in them may be 
recognized especially strengthened bands which are described as ligaments. This, 
however, is not the only method of formation of ligaments. In some cases by 
modification of, or derivations from, the tendons surrounding the joint, additional 
ligamentous bands are provided to further strengthen the articulations. 

In several of the movable joints the mesoderm which originally existed between 
the ends of the bones does not become completely absorbed — a portion of it 
persists and forms an articular disk. These disks may be intimately associated in 
their development with the muscles surrounding the joint, e. g., the menisci of the 
knee-joint, or with cartilaginous elements, representatives of skeletal structures, 
which are vestigial in human anatomy, e. g., the articular disk of the sterno- 
clavicular joint. 



284 



SYNDESMOLOGY 
CLASSIFICATION OF JOINTS. 



The articulations are divided into three classes: synarthroses or immovable, 
amphiarthroses or slightly movable, and diarthroses or freely movable, joints. 

Synarthroses (immovable articulations). — Synarthroses include all those articu- 
lations in which the surfaces of the bones are in almost direct contact, fastened 
together by intervening connective tissue or hyaline cartilage, and in which there 
is no appreciable motion, as in the joints between the bones of the skull, excepting 
those of the mandible. There are four varieties of synarthrosis : sutura, schindylesis, 
gomphosis, and synchondrosis. 

Sutura.^ — Sutura is that form of articulation where the contiguous margins of the 
bones are united by a thin layer of fibrous tissue; it is met wdth only in the skull 
(Fig. 296) . When the margins of the bones are connected by a series of processes, 
and indentations interlocked together, the articulation is termed a true suture 
(sutura vera); and of this there are three varieties: sutura dentata, serrata, and 
limbosa. The margins of the bones are not in direct contact, being separated by a 
thin layer of fibrous tissue, continuous externally with the pericranium, internally 
with the dura mater. The sutura dentata is so called from the tooth-like form of 
the projecting processes, as in the suture between the parietal bones. In the 



Periosteum 



Suturai ligament 



Cartilage 





Fig. 296.— Section across the sagittal suture. 



Fig. 297. 



Perichondrium 

Periosteum 

—Section through occipitosphenoid synchon- 
drosis of an infant. 



sutura serrata the edges of the bones are serrated like the teeth of a fine saw, as 
between the two portions of the frontal bone. In the sutura limbosa, there is besides 
the interlocking, a certain degree of bevelling of the articular surfaces, so that the 
bones overlap one another, as in the suture between the parietal and frontal bones. 
When the articulation is formed by roughened surfaces placed in apposition with 
one another, it is termed a false suture (sutura notha), of which there are two kinds: 
the sutura squamosa, formed by the overlapping of contiguous bones by broad 
bevelled margins, as in the squamosal suture between the temporal and parietal, 
and the sutura harmonia, where there is simple apposition of contiguous rough 
surfaces, as in the articulation between the maxillae, or between the horizontal 
parts of the palatine bones. 

Schindylesis. — Schindylesis is that form of articulation in which a thin plate 
of bone is received into a cleft or fissure formed by the separation of two lamiuEe in 
another bone, as in the articulation of the rostrum of the sphenoid and perpendicular 
plate of the ethmoid with the vomer, or in the reception of the latter in the fissure 
between the maxillae and between the palatine bones. 

Gomphosis. — Gomphosis is articulation by the insertion of a conical process into 
a socket; this is not illustrated by any articulation between bones, properly so 
called, but is seen in the articulations of the roots of the teeth with the alveoli 
of the mandible and maxillse. 

Synchondrosis. — Where the connecting medium is cartilage the joint is termed 
a synchondrosis (Fig. 297). This is a temporary form of joint, for the cartilage 
is converted into bone before adult life. Such joints are found between the 
epiphyses and bodies of long bones, between the occipital and the sphenoid at, 
and for some years after, birth, and between the petrous portion of the temporal 
and the jugular process of the occipital. 



CLASSIFICATION OF JOINTS 



285 



Ligament^ jy^iy'^X'r^fS'-.fv/^^t/i 

Disc of 
fibrocartilage 
Articular cartilage 







Amphiarthroses (slightb/ movable articulations).— In these articulations the 
contiguous bony surfaces are either connected by broad flattened disks of fibro- 
cartilage, of a more or less complex struc- 
ture, as in the articulations between the 
bodies of the vertebrae; or are united by an 
interosseous ligament, as in the inferior 
tibiofibular articulation. The first form is 
termed a symphysis (P'ig. 298), the second 
a syndesmosis. 

Diarthroses {freely movable articulations). 
— This class includes the greater number 
of the joints in the body. In a diarthrodial joint the contiguous bony surfaces 
are covered with articular cartilage, and connected by ligaments lined by synovial 
membrane (Fig. 299). The joint may be divided, completely or incomjpletely, 
by an articular di'sk or meniscus, the periphery of which is continuous with 
the fibrous capsule while its free surfaces are covered by synovial membrane 
(Fig. 300). 






Fio. 298. — Diagrammatic section of a symphysis. 




Articular cartilage 

Synovial ' 

stratum \ Articular 
Fibrosis I capsule 
stratum . 




Fig. 299. — Diagrammatic section of a diarthrodial joint. 



Fig. 



Synovial stratum 

Articular cartilage 
Articular disk 



Fibrous stratum 



300. — Diagrammatic section of a diarthrodial 
joint, with an articular disk. 



The varieties of joints in this class have been determined by the kind of motion 
permitted in each. There are two varieties in which the movement is uniaxial, that 
is to say, all movements take place around one axis. In one form, the ginglymus, 
this axis is, practically speaking, transverse; in the other, the trochoid or pivot- 
joint, it is longitudinal. There are two varieties where the movement is biaxial, 
or around two horizontal axes at right angles to each other, or at any intervening 
axis between the two. These are the condyloid and the saddle-joint. There is 
one form where the movement is polyaxial, the enarthrosis or ball-and-socket joint; 
and finally there are the arthrodia or gliding joints. 

Ginglymus or Hinge-joint. — In this form the articular surfaces are moulded 
to each other in such a manner as to permit motion only in one plane, forward 
and backward, the extent of motion at the same time being considerable. The 
direction which the distal bone takes in this motion is seldom in the same plane 
as that of the axis of the proximal bone; there is usually a certain amount of devia- 
tion from the straight line during flexion. The articular surfaces are connected 
together by strong collateral ligaments, w^hich form their chief bond of union. 
The best examples of ginglymus are the interphalangeal joints and the joint between 
the humerus and ulna; the knee- and ankle-joints are less typical, as they allow 
a Slight degree of rotation or of side-to-side movement in certain positions of the 
limb. 

Trochoid or Pivot-joint (articulatio trochoidea; rotary joint) . — "VMiere the movement 
is limited to rotation, the joint is formed by a pivot-like process turning within 



286 SYNDESMOLOGY 

a ring, or a ring on a pivot, the ring being formed partly of bone, partly of ligament. 
In the proximal radioulnar articulation, the ring is formed by the radial notch 
of the ulna and the annular ligament; here, the head of the radius rotates within 
the ring. In the articulation of the odontoid process of the axis with the atlas 
the ring is formed in front by the anterior arch, and behind by the transverse 
ligament of the atlas; here, the ring rotates around the odontoid process. 

Condyloid Articulation {articulatio ellipsoidea) .■ — In this form of joint, an ovoid 
articular surface, or condyle, is received into an elliptical cavity in such a manner 
as to permit of flexion, extension, adduction, abduction, and circumduction, but 
no axial rotation. The wrist-joint is an example of this form of articulation. 

Articulation by Reciprocal Reception (articulatio sellaris; saddle-joint).- — In this 
variety the opposing surfaces are reciprocally concavo-convex. The movements 
are the same as in the preceding form; that is to say, flexion, extension, adduction, 
abduction, and circumduction are allowed ; but no axial rotation. The best example 
of this form is the carpometacarpal joint of the thumb. 

Enarthrosis {hall-and-socket joints) . — Enarthrosis is a joint in which the distal 
bone is capable of motion around an indefinite number of axes, which have one 
common center. It is formed by the reception of a globular head into a cup-like 
cavity, hence the name "ball-and-socket." Examples of this form of articulation 
are found in the hip and shoulder. 

Arthrodia (gliding joints) is a joint which admits of only gliding movement; it 
is formed by the apposition of plane surfaces, or one slightly concave, the other 
slightly convex, the amount of motion between them being limited by the ligaments 
or osseous processes surrounding the articulation. It is the form present in the 
joints between the articular processes of the vertebrae, the carpal joints, except 
that of the capitate with the navicular and lunate, and the tarsal joints with the 
exception of that between the talus and the navicular. 



THE KINDS OF MOVEMENT ADMITTED IN JOINTS. 

The movements admissible in joints may be divided into four kinds: gliding 
and angular movements, circumduction, and rotation. These movements are often, 
however, more or less combined in the various joints, so as to produce an infinite 
variety, and it is seldom that only one kind of motion is found in any particular 
joint. 

Gliding Movement.- — Gliding movement is the simplest kind of motion that can 
take place in a joint, one surface gliding or moving over another without any 
angular or rotatory movement. It is common to all movable joints; but in some, 
as in most of the articulations of the carpus and tarsus, it is the only motion per- 
mitted. This movement is not confined to plane surfaces, but may exist between 
any two contiguous surfaces, of whatever form. 

Angular Movement. — Angular movement occurs only between the long bones, 
and by it the angle , between the two bones is increased or diminished. It may 
take place: (1) forward and backward, constituting flexion and extension; or (2) 
toward and from the median plane of the body, or, in the case of the fingers or 
toes, from the middle line of the hand or foot, constituting adduction and abduction. 
The strictly ginglymoid or hinge-joints admit of flexion and extension only. Abduc- 
tion and adduction, combined with flexion and extension, are met with in the more 
movable joints; as in the hip, the shoulder, the wrist, and the carpometacarpal 
joint of the thumb. 

Circumduction. — Circumduction is that form of motion which takes place between 
the head of a bone and its articular cavity, when the bone is made to circumscribe 
a conical space; the base of the cone is described by the distal end of the bone. 



ARTICULATIONS OF THE VERTEBRAL COLUMN 287 

the apex is in the articular cavity; this kind of motion is best seen in the shoulder- 
and hip-joints. 

Rotation.— Rotation is a form of movement in which a bone moves around a 
central axis without undergoing any displacement from this axis; the axis of rota- 
tion may lie in a separate bone, as in the case of the 'pivot formed by the odontoid 
process of the axis yertebrse around which the atlas turns; or a bone may rotate 
around its own longitudinal axis, as in the rotation of the humerus at the shoulder- 
joint; or the axis of rotation may not be quite parallel to the long axis of the 
bone, as in the movement of the radius on the ulna during pronation and supina- 
tion of the hand, where it is represented by a line connecting the center of the 
head of the radius above with the center of the head of the ulna below. 

Ligamentous Action of Muscles.— The movements of the different joints of a hmb are combined 
by means of the long muscles passing over more than one joint. These, when relaxed and stretched 
to their greatest extent, act as elastic hgaments in restraining certain movements of one joint, 
except when combined with corresponding movements of the other— the latter movements being 
usually in the opposite direction. Thus the shortness of the hamstring muscles prevents com- 
plete flexion of the hip, unless the knee-joint is also flexed so as to bring their attachments nearer 
together. The uses of this arrangement are threefold: (1) It coordinates the kinds of move- 
ments which are the most habitual and necessary, and enables them to be performed with the 
least expenditure of power. (2) It enables the short muscles which pass over only one joint to 
act upon more than one. (3) It provides the joints with hgaments which, while they are of very 
great power in resisting movements to an extent incompatible with the mechanism of the joint, 
at the same time spontaneously yield when necessary. 

The articulations may be grouped into those of the trunk, and those of the upper 
and lower extremities. 

ARTICULATIONS OF THE TRUNK. 

These may be divided into the following groups, viz.: 

I. Of the Vertebral Column. VI. Of the Cartilages of the Ribs with the 

II. Of the Atlas with the Axis. Sternum, and with Each Other. 

III. Of the Vertebral Column with VII. Of the Sternum. 

the Cranium. VIII. Of the Vertebral Column with the 

IV. Of the Mandible. Pelvis. 
V. Of the Ribs with the Vertebra. IX. Of the Pelvis. 

I. Articulations of the Vertebral Column. 

The articulations of the vertebral column consist of (1) a series of amphi- 
arthrodial joints between the vertebral bodies, and (2) a series of diathrodial 
joints between the vertebral arches. 

1. Articulations of Vertebral Bodies {intercentral ligaments). — The articulations 
between the bodies of the vertebrae are amphiarthrodial joints, and the individual 
vertebrae move only slightly on each other. When, however, this slight degree 
of movement between the pairs of bones takes place in all the joints of the vertebral 
column, the total range of movement is very considerable. The ligaments of these 
articulations are the following: 

The Anterior Longitudinal. The Posterior Longitudinal. 

The Intervertebral Fibrocartilages. 

The Anterior Longitudinal Ligament {ligamentum longitudinale anterius; anterior 
common ligament) (Figs. 301, 312). — The anterior longitudinal ligament is a broad 
and strong band of fibers, which extends along the anterior surfaces of the bodies 
of the vertebrae, from the axis to the sacrum. It is broader below than above, 



288 



SYNDESMOLOGY 



thicker in the thoracic than in the cervical and kimbar regions, and somewhat 
thicker opposite the bodies of the vertebrae than opposite the intervertebral fibro- 
cartilages. It is attached, above, to the body of the axis, where it is continuous 
with the anterior atlantoaxial ligament, and extends down as far as the upper 
part of the front of the sacrum. It consists of dense longitudinal fibers, which 
are intimately adherent to the intervertebral fibrocartilages and the prominent 
margins of the vertebrae, but not to the middle parts of the bodies. In the latter 
situation the ligament is thick and serves to fill up the concavities on the anterior 
surfaces, and to make the front of the vertebral column more even. It is composed 
of several layers of fibers, which vary in length, but are closely interlaced with 
each other. The most superficial fibers are the longest and extend between four 
or five vertebrae. A second, subjacent set extends between two or three vertebrae; 
while a third set, the shortest and deepest, reaches from one vertebra to the next. 
At the sides of the bodies the ligament consists of a few short fibers which pass 
from one vertebra to the next, separated from the concavities of the vertebral 
bodies by oval apertures for the passage of vessels. 







Fia. 301. — Median sagittal section of two lumbar vertebrae and their ligaments. 

The Posterior Longitudinal Ligament {ligameutiim longitudinale posterius; posterior 
common ligament) (Figs. 801, 302).— The posterior longitudinal ligament is situated 
within the vertebral canal, and extends along the posterior surfaces of the bodies 
of the vertebrae, from the body of the axis, where it is continuous with the membrana 
tectoria, to the sacrum. It is broader above than below, and thicker in the thoracic 
than in the cervical and lumbar regions. In the situation of the intervertebral 
fibrocartilages and contiguous margins of the vertebrae, where the ligament is more 
intimately adherent, it is broad, and in the thoracic and lumbar regions presents 
a series of dentations with intervening concave margins ; but it is narrow and thick 
over the centers of the bodies, from which it is separated by the basivertebral 
veins. This ligament is composed of smooth, shining, longitudinal fibers, denser 
and more compact than those of the anterior ligament, and consists of superficial 
layers occupying the interval between three or four vertebrae, and deeper layers 
which extend between adjacent vertebrae. 



ARTICULATIONS OF THE VERTEBRAL COLUMN 



289 



Pedicle (cul) 



Intervertebral 
fibrocartilage 



The Intervertebral Fibrocartilages {fihrocartilagines intervertebrales; intervertebral 
disks) (Figs. ;^()1, 313) .—The intervertebral fibrocartilages are interposed between 
the adjacent snrfaces of the bodies of the vertebne, from the axis to the sacrum, 
and form the chief bonds of connection between the vertebrae. They vary in shape, 
size, and thickness, in different parts of the vertebral column. In shape and size 
they correspond with the surfaces of the bodies between which they are placed, 
except in the cervical region, where they are slightly smaller from side to side than 
the corresponding bodies. In thickness they vary not only in the difi'erent regions 
of the column, but in different parts of the same fibrocartilage; they are thicker 
in front than behind in the cervical and lumbar 
regions, and thus contribute to the anterior con- 
vexities of these parts of the column ; while they 
are of nearly uniform thickness in the thoracic 
region, the anterior concavity of this part of 
the column being almost entirely owing to the 
shape of the vertebral bodies. The interverte- 
bral fibrocartilages constitute about one-fourth 
of the length of the vertebral column, exclusive 
of the first two vertebrae; but this amount is 
not equally distributed between the various 
bones, the cervical and lumbar portions having, 
in proportion to their length, a much greater 
amount than the thoracic region, with the result 
that these parts possess greater pliancy and 
freedom of movement. The intervertebral 
fibrocartilages are adherent, by their surfaces, 
to thin layers of hyaline cartilage which cover 
the upper and under surfaces of the bodies of 
the vertebrae; in the lower cervical vertebrae, 
however, small joints lined by synovial membrane are occasionally present between 
the upper surfaces of the bodies and the margins of the fibrocartilages on either 
side. By their circumferences the intervertebral fibrocartilages are closely con- 
nected in front to the anterior, and behind to the posterior, longitudinal liga- 
ments. In the thoracic region they are joined laterally, by means of the inter- 
articular ligaments, to the heads of those ribs which articulate with two vertebrae. 




Fig. 302. — Posterior longitudinal ligament, in 
the thoracic region. 



Structure of the Intervertebral Fibrocartilages. — Each is composed, at its circumference, of 
laminae of fibrous tissue and fibrocartilage, forming the annulus fibrosus; and, at its center, of 
a soft, pulpy, highly elastic substance, of a yellowish color, which projects considerably above 
the surrounding level when the disk is divided horizontally. This pulpy substance {nucleus 
pulposus), especially well-developed in the lumbar region, is the remains of the notochord. The 
laminae are arranged concentrically; the outermost consist of ordinary fibrous tissue, the others 
of white fibrocartilage. The laminae are not quite vertical in their direction, those near the cir- 
cumference being curved outward and closely approximated; while those nearest the center 
curve in the opposite direction, and are somewhat more widely separated. The fibers of which 
each lamina is composed are directed, for the most part, obliquely from above downward, the 
fibers of adjacent laminae passing in opposite directions and varying in every layer; so that the 
fibers of one layer are directed across those of another, Uke the hmbs of the letter X. This laminar 
arrangement belongs to about the outer half of each fibrocartilage. The pulpy substance presents 
no such arrangement, and consists of a fine fibrous matrix, containing angular cells united to 
form a reticular structure. 

The intervertebral fibrocartilages are important shock absorbers. Under pressure the highly 
elastic nucleus pulposus becomes flatter and broader and pushes the more resistant fibrous laminae 
outward in all directions. 

2. Articulations of Vertebral Arches. — The joints between the articular pro- 
cesses of the vertebrae belong to the arthrodial variety and are enveloped by 
19 



290 



SYNDESMOLOGY 



capsules lined by synovial membranes; while the laminae, spinous and transverse 
processes are connected by the following ligaments: 



The Ligamenta Flava. 
The Supraspinal. 



The Ligamentum Nuchae. 
The Interspinal. 
The Intertransverse. 



Pedicle {cut) 



The Articular Capsules (capsular articulares; capsular ligamerits) (Fig. 301).- — ■ 
The articular capsules are thin and loose, and are attached to the margins of the 
articular processes of adjacent vertebrae. They are longer and looser in the cervical 
than in the thoracic and lumbar regions. 

The Ligamenta Flava {ligamenta suhflara, Fig. 303).- — The ligamenta flava connect 
the laminae of adjacent vertebrae, from the axis to the first segment of the sacrum. 
They are best seen from the interior of the vertebral canal; when looked at from the 
outer surface they appear short, being overlapped by the laminae. Each ligament 
consists of two lateral portions which commence one on either side of the roots 
of the articular processes, and extend backward to the point where the laminae 
meet to form the spinous process ; the posterior margins of the two portions are in 
contact and to a certain extent united, slight intervals being left for the passage 
of small vessels. Each consists of yellow elastic tissue, the fibers of which, almost 

perpendicular in direction, are at- 
tached to the anterior surface of 
the lamina above, some distance 
from its inferior margin, and to the 
posterior surface and upper margin 
of the lamina below. In the cervical 
region the ligaments are thin, but 
broad and long; they are thicker in 
the thoracic region, and thickest in 
the lumbar region. Their marked 
elasticity serves to preserve the up- 
right posture, and to assist the 
vertebral column in resuming it 
after flexion. 

The Supraspinal Ligament {liga- 
mentum supraspinaJe; supraspinous 
ligament) (Fig. 301). — The supra- 
spinal ligament is a strong fibrous 
cord, which connects together the 
apices of the spinous processes from 
the seventh cervical vertebra to the sacrum; at the points of attachment to the 
tips of the spinous processes fibrocartilage is developed in the ligament. It is 
thicker and broader in the lumbar than in the thoracic region, and intimately 
blended, in both situations, with the neighboring fascia. The most superficial 
fibers of this ligament extend over three or four vertebrae; those more deeply 
seated pass between two or three vertebrae ; while the deepest connect the spinous 
processes of neighboring vertebrae. Between the spinous processes it is continuous 
with the interspinal ligaments. It is continued upward to the external occipital 
protuberance and median nuchal line, as the ligamentum nuchae. 

The Ligamentum Nuchas. — The ligamentum nuchae is a fibrous membrane, which, 
in the neck, represents the supraspinal ligaments of the lower vertebrae. It extends 
from the external occipital protuberance and median nuchal line to the spinous 
process of the seventh cervical vertebra. From its anterior border a fibrous lamina 
is given off, which is attached to the posterior tubercle of the atlas, and to the 
spinous processes of the cervical vertebrae, and forms a septum between the muscles 




Lamina 



FiQ. 303. — Vertebral arches of three thoracic vertebrae 
viewed from the front. 



ARTICULATIONS OF THE VERTEBRAL COLUMN 291 

on either side of the neck. In man it is merely the rudiment of an important elastic 
ligament, which, in some of the lower animals, serves to sustain the weight of the 
head. 

The Interspinal Ligaments {ligamenta inter syinalia; interspinous ligaments) 
(Fig. 301).— The interspinal ligaments thin and membranous, connect adjoining 
spinous processes and extend from the root to the apex of each process. They 
meet the ligamenta flava in front and the supraspinal ligament behind. They 
are narrow and elongated in the thoracic region; broader, thicker, and quadrilateral 
in form in the lumbar region; and only slightly developed in the neck. 

The Intertransverse Ligaments {ligamenta intertransversaria) . — The intertransverse 
ligaments are interposed between the transverse processes. In the cervical region 
they consist of a few irregular, scattered fibers; in the thoracic region they are 
rounded cords intimately connected with the deep muscles of the back; in the 
lumbar region they are thin and membranous. 

Movements.— The movements permitted in the vertebral column are: flexion, extension, 
lateral movement, circumduction, and rotation. 

In flexion, or movement forward, the anterior longitudinal Hgament is relaxed, and the inter- 
vertebral fibrocartilages are compressed in front; while the posterior longitudinal ligament, the 
ligamenta flava, and the inter- and supraspinal ligaments are stretched, as well as the posterior 
fibers of the intervertebral fibrocartilages. The interspaces between the laminje are widened, 
and the inferior articular processes ghde upward, upon the superior articular processes of the 
subjacent vertebra?. Flexion is the most extensive of all the movements of the vertebral column, 
and is freest in the lumbar region. 

In extension, or movement backward, an exactly opposite disposition of the parts takes place. 
This movement is limited by the anterior longitudinal Ugament, and by the approximation of 
the spinous processes. It is freest in the cervical region. 

In lateral movement, the sides of the intervertebral fibrocartilages are compressed, the extent 
of motion being Umited by the resistance offered by the surrounding hgaments. This movement 
may take place in any part of the column, but is freest in the cervical and lumbar regions. 

Circumduction is very limited, and is merely a succession of the preceding movements. 

Rotation is produced by the twisting of the intervertebral fibrocartilages; this, although only 
shght between any two vertebrae, allows of a considerable extent of movement when it takes place 
in the whole length of the column, the front of the upper part of the column being turned to one 
or other side. This movement occurs to a slight extent in the cervical region, is freer in the upper 
part of the thoracic region, and absent in the lumbar region. 

The extent and variety of the movements are influenced by the shape and direction of the 
articular surfaces. In the cervical region the upward incHnation of the superior articular surfaces 
allows of free flexion and extension. Extension can be carried farther than flexion; at the upper 
end of the region it is checked by the locking of the posterior edges of the superior atlantal facets 
in the condyloid fossae of the occipital bone; at the lower end it is limited by a mechanism whereby 
the inferior articular processes of the seventh cervical vertebra slip into grooves behind and 
below the superior articular processes of the first thoracic. Flexion is arrested just beyond the 
point where the cervical convexity is straightened; the movement is checked by the apposition 
of the projecting lower lips of the bodies of the vertebrae with the shelving surfaces on the bodies 
of the subjacent vertebrae. Lateral flexion and rotation are free in the cervical region; they are, 
however, always combined. The upward and medial incUnations of the superior articular surfaces 
impart a rotatory movement during lateral flexion, while pure rotation is prevented by the slight 
medial slope of these surfaces. 

In the thoracic region, notably in its upper part, all the movements are Hmited in order to 
reduce interference with respiration to a minimum. The almost complete absence of an upward 
incUnation of the superior articular surfaces prohibits any marked fle.xion, while extension is 
checked by the contact of the inferior articular margins with the laminae, and the contact of the 
spinous processes with one another. The mechanism between the seventh cervical and the first 
thoracic vertebrae, which limits extension of the cervical region, will also serve to limit flexion of 
the thoracic region when the neck is extended. Rotation is free in the thoracic region: the 
superior articular processes are segments of a cylinder whose axis is in the mid-ventral line of the 
vertebral bodies. The direction of the articular facets would allow of free lateral flexion, but 
this movement is considerably limited in the upper part of the region by the resistance of the 
ribs and sternum. 

In the lumbar region flexion and extension are free. Flexion can be carried farther than exten- 
sion, and is possible to just beyond the straightening of the lumbar curve; it is, therefore, greatest 
at the lowest part where the curve is sharpest. The inferior articular facets are not in close appo- 



292 



SYNDESMOLOGY 



sition with the superior facets of the subjacent vertebrae, and on this account a considerable 
amount of lateral flexion is permitted. For the same reason a shght amount of rotation can be 
carried out, but this is so soon checked by the interlocking of the articular surfaces that it is 
neghgible. 

The principal muscles which produce flexion are the Sternocleidomastoideus, Longus capitis, 
and Longus coUi; the Scaleni; the abdominal muscles and the Psoas major. Extension is produced 
by the intrinsic muscles of the back, assisted in the neck bj- the Splenius, Semispinales dorsi and 
cervicis, and the Miiltifidus. Lateral motion is produced by the intrinsic muscles of the back 
by the Splenius, the Scaleni, the Quadratus lumborum, and the Psoas major, the muscles of one 
side only acting; and rotation by the action of the following muscles of one side only, viz., the 
Sternocleidomastoideus, the Longus capitis, the Scaleni, the Multifidus, the Semispinalis capitis, 
and the abdominal muscles. 



II. Articulation of the Atlas with the Epistropheus or Axis (Articulatio 

Atlantoepistrophica) . 

The articulation of the atlas with the axis is of a complicated nature, com- 
prising no fewer than four distinct joints. There is a pivot articulation between 
the odontoid process of the axis and the ring formed by the anterior arch and 
the tranverse ligament of the atlas (see Fig. 306); here there are two joints: one 
between the posterior surface of the anterior arch of the atlas and the front of 
the odontoid process; the other between the anterior surface of the ligament and 
the back of the process. Between the articular processes of the two bones there 
is on either side an arthrodial or gliding joint. The ligaments connecting these 
bones are: 



Two Articular Capsules. 
The Anterior Atlantoaxial. 



The Posterior Atlantoaxial. 
The Transverse. 




Atlanto- 

occipital C -Articular capsule 

■[ and 

\iiynovial membrane 



Articular capsule 

and 
synodal membrane 



Fig. 304. — Anterior atlantooccipital membrane and atlantoaxial ligament. 

The Articular Capsules {capsultr articulares ; capsular ligamenfs). — The articular 
capsules are thin and loose, and connect the margins of the lateral masses of the 
atlas with those of the posterior articular surfaces of the axis. Each is strength- 
ened at its posterior and medial part by an accessory ligament^ which is attached 



ARTICULATIOX OF THE ATLAS WITH THE EPISTROPHEUS OR AXIS 293 

below to the body of the axis near the base of the odontoid process, and above 
to the lateral mass of the atlas near the transverse ligament. 

The Anterior Atlantoaxial Ligament (Fig. 304).— This ligament is a strong mem- 
brane, fixed, above, to the lower border of the anterior arch of the atlas; below, 
to the front of the body of the axis. It is strengthened in the middle line bv a 




Arch for passage of 
vertebral artery 
and first cervical 
nerve 



Fig. 305. — Posterior atlantooccipital membrane and atlantoaxial ligament. 

rounded cord, which connects the tubercle on the anterior arch of the atlas to the 
body of the axis, and is a continuation upward of the anterior longitudinal liga- 
ment. The ligament is in relation, in front, with the Longi capitis. 




Fig. 300. — Articulation between odontoid process and atlas. 



The Posterior Atlantoaxial Ligament (Fig. 305). — This ligament is a broad, thin 
membrane attached, above, to the lower border of the posterior arch of the atlas; 
heloic, to the upper edges of the lamimie of the axis. It supplies the place of 
the ligamenta flava, and is in relation, behind, with the Obliqui capitis inferiores. 

The Transverse Ligament of the Atlas {ligamentum transversum ailantis) (Figs. 
306, 307, 30S).— The transverse ligament of the atlas is a thick, strong band, which 



294 



SYNDESMOLOGY 




Apical odontoid 
ligament 



Atlanta. (^'^''''^""'"P^'^' 
occipital I gu^Q^iai membrane 



. , . , Artindar capsule 
Atlanta-} „,,^ 

axial y synovial membrane 



Fig. 307. — Membrana tectoria, transverse, and alar ligaments. 



Anterior atlanto- 
occipital membrane 

3Iembrana tectoriu 

Crus superiws of 

transverse ligament 

Apical odont. lig 

Ant. arch of atlas 

Odontoid process 
of axis 
Articidar cavi 

Transverse ligament 

Anterior atlanto- 
axial ligament 



Superficial layer of membrana. tectoria 
Canalis hypoglossi 



Posterior atlanto- 
occipital membrane 

Posterior arch 
of atlas 

iuboccipital nerve 



Intervertebral 
fbrocartilage 



Anterior longitudinal 
ligament 




Posterior longitudinal ligament 
Fig. 308 —Median sagittal section through the occipital bone and first three cervical vertebrae. (Spalteholz.) 



ARTICULATIONS OF THE VERTEBRAL COLUMN WITH THE CRANIUM 295 

arches across the ring of the atlas, and retains the odontoid process in contact with 
the anterior arch. It is concave in front, convex behind, broader and thicker in 
the middle than at the ends, and firmly attached on either side to a small tubercle 
on the medial surface of the lateral mass of the atlas. As it crosses the odontoid 
process, a small fasciculus (cms superius) is prolonged upward, and another (cms 
injerius) downward, from the superficial or posterior fibers of the ligament. The 
former is attached to the basilar part of the occipital bone, in close relation with 
the membrana tectoria; the latter is fixed to the posterior surface of the l)ody 
of the axis; hence, the whole ligament is named the cruciate ligament of the atlas. 
The transverse ligament divides the ring of the atlas into two unequal parts: 
of these, the posterior and larger ser\'es for the tcansmission of the medulla spinalis 
and its membranes and the accessory nerves; the anterior and smaller contains 
the odontoid process. The neck of the odontoid process is constricted where it is 
embraced posteriorly by the transverse ligament, so that this ligament suffices 
to retain the odontoid process in position after all the other ligaments have been 
divided. 

Synovial Membranes. — There is a sjTiovial membrane for each of the four joints; the joint 
cavity between the odontoid i)rocess and the transverse ligament is often continuous with those 
of the atlantooccipital articulations. 

Movements. — The opposed articular surfaces of the atlas and axis are not reciprocally curved; 
both surfaces are convex in their long axes. When, therefore, the upper facet glides forward 
on the lower it also descends; the fibers of the articular capsule are relaxed in a vertical direc- 
tion, and will then permit of movement in an antero-posterior direction. By this means a 
shorter capsule suffices and the strength of the joint is materially increased.^ 

This joint allows the rotation of the atlas (and, with i., the skull) upon the axis, the extent 
of rotation being limited by the alar ligaments. 

The principal muscles by which these movements are produced are the Sternocleidomastoideus 
and Semispinalis capitis of one side, acting with the Longus capitis, Splenius, Longissimus capitis, 
Rectus capitis posterior major, and ObUqui capitis superior and inferior of the other side. 

III. Articulations of the Vertebral Column with the Cranium. 

The ligaments connecting the vertebral column with the cranium may be 
divided into two sets: those uniting the atlas with the occipital bone, and those 
connecting the axis with the occipital ])one. 

Articulation of the Atlas with the Occipital Bone {articulatio atlantodccipitalis) . 
— The articulation between the atlas and the occipital bone consists of a pair of 
condyloid joints. The ligaments connecting the bones are: 

Two Articular Capsules. The Posterior Atlantooccipital 

The Anterior Atlantooccipital membrane. 

membrane. • Two Lateral Atlantooccipital. 

The Articular Capsules (capsidop articulares; capsular ligaments). — The articular 
capsules surround the condyles of the occipital bone, and connect them with the 
articular processes of the atlas: they are thin and loose. 

The Anterior Atlantooccipital Membrane {memhrana atlantooccipitalis anterior; 
anterior atlantooccipital ligament) (Fig. 304).— The anterior atlantooccipital mem- 
brane is broad and composed of densely woven fibers, which pass between the 
anterior margin of the foramen magnum above, and the upper border of the 
anterior arch" of the atlas below; laterally, it is continuous with the articular 
capsules; in front, it is strengthened in the middle line by a strong, rounded 

» Corner ("The Phvsiologv of the Atlanto-axial Joints." Journal of Anatomy and Physiology, vol xli) states that 
the movements whicVl take place at these articulations are of a complex nature. The hrst part of the movement is 
an eccentric or asvmmetrical one; the atlanto-axial joint of the side to which the head is moved is faxed, or practically 
fixed, by the muscles of the neck, and forms the center of the movement, while the opposite atlantal facet is carried 
downward and forward on the corresponding axial facet. The second part of the movement is centric and symmetrical, 
the odontoid process forming the axis of the movement 



296 SYNDESMOLOGY 

cord, which connects the basilar part of the occipital bone to the tubercle on the 
anterior arch of the atlas. This membrane is in relation in front with the Recti 
capitis anteriores, hehind with the alar ligaments. 

The Posterior Atlantooccipital Membrane (membrana atlantodccipitalis posterior; 
posterior atlaniooccipital ligament) (Fig. 305). — The posterior atlantooccipital mem- 
brane, broad but thin, is connected above, to the posterior margin of the foramen 
magnum; below, to the upper border of the posterior arch of the atlas. On either 
side this membrane is defective below, over the groove for the vertebral artery, 
and forms with this groove an opening for the entrance of the artery and the 
exit of the suboccipital nerve. The free border of the membrane, arching over 
the artery and nerve, is sometimes ossified. The membrane is in relation, behind, 
with the Recti capitis posteriores minores and Obliqui capitis superiores; in /ro/z^, 
with the dura mater of the vertebral canal, to which it is intimately adherent. 

The Lateral Ligaments. — The lateral ligaments are thickened portions of the 
articular capsules, reinforced by bundles of fibrous tissue, and are directed obliquely 
upward and medialward; they are attached above to the jugular processes of the 
occipital bone, and below, to the bases of the transverse processes of the atlas. 

Ssmovial Membranes. — There are two synovial membranes: one lining each of the articular 
capsules. The joints frequently communicate with that between the posterior surface of the 
odontoid process and the transverse hgament of the atlas. 

Movements. — The movements permitted in this joint are (a) flexion and extension, which 
give rise to the ordinary forward and backward nodding of the head, and (b) slight lateral motion 
to one or other side. Flexion is produced mainly by the action of the Longi capitis and Recti 
capitis anteriores; extension by the Recti capitis posteriores major and minor, the Obliquus su- 
perior, the Semispinahs capitis, Splenius capitis, Sternocleidomastoideus, and upper fibers of the 
Trapezius. The Recti laterales are concerned in the lateral movement, assisted bj' the Trapezius, 
Splenius capitis, Semispinalis capitis, and the Sternocleidomastoideus of the same side, all acting 
together. 

Ligaments Connecting the Axis with the Occipital Bone. — 

The INIembrana Tectoria. Two Alar. The Apical Odontoid. 

The Membrana Tectoria (occipitoaxial ligament) (Figs. 307, 308). — The mem- 
brana tectoria is situated within the vertebral canal. It is a broad, strong bands 
which covers the odontoid process and its ligaments, and appears to be a prolon- 
gation upward of the posterior longitudinal ligament of the vertebral column. It 
is fixed, below, to the posterior surface of the body of the axis, and, expanding as 
it ascends, is attached to the basilar groove of the occipital bone, in front of the 
foramen magnum, where it blends with the cranial dura mater. Its anterior sur- 
face is in relation with the transverse ligament of the atlas, and its posterior 
surface with the dura mater. 

The Alar Ligaments {Ugamenta alaria; odontoid ligaments) (Fig. 307).- — The alar 
ligaments are strong, rounded cords, which arise one on either side of the upper 
part of the odontoid process, and, passing obliquely upward and lateralward, are 
inserted into the rough depressions on the medial sides of the condyles of the occipi- 
tal bone. In the triangular interval between these ligaments is another fibrous 
cord, the apical odontoid ligament (Fig. 308), which extends from the tip of the odon- 
toid process to the anterior margin of the foramen magnum, being intimately 
blended with the deep portion of the anterior atlantooccipital membrane and 
superior crus of the transverse ligament of the atlas. It is regarded as a rudimentary 
intervertebral fibrocartilage, and in it traces of the notochord may persist. The 
alar ligaments limit rotation of the cranium and therefore receive the name of 
check ligaments. 

In addition to the ligaments which unite the atlas and axis to the skull, 
the ligamentum nucha? (page 290) must be regarded as one of the ligaments 
connecting the vertebral column with the cranium. 



ARTICULATION OF THE MANDIBLE 



297 



IV. Articulation of the Mandible (Articulatio Mandibularis ; Temporo- 
mandibular Articulation). 

This is a ginglymo-arthrodial joint; the parts entering into its formation on 
either side are: the anterior part of the mandibular fossa of the temporal bone 
and the articular tubercle above; and the condyle of the man(Uble below. The 
ligaments of the joint are the following: 

The Articular Capsule. The Sphenomandibular. 

The Temporomandibular. ^ The Articular Disk. 

The Stylomandibular. 

The Articular Capsule (capsida articularis; cajysular ligament) .—The articular 
capsule is a thin, loose envelope, attached above to the circumference of the 
mandibular fossa and the articular tubercle immediately in front; below, to the 
neck of the condyle of the mandible. 



V \ 




Fia. 309. — Articulation of the mandible. Lateral aspect. 

The Temporomandibular Ligament (ligamentum temporomandihidare: external 
lateral ligament) (Fig. ;^)09). — The temporomandibular ligament consists of two 
short, narrow fasciculi, one in front of the other, attached, above, to the lateral 
surface of the zygomatic arch and to the tubercle on its lower border; below, 
to the lateral surface and posterior border of the neck of the mandible. It is broader 
above than below, and its fibers are directed obliquely downward and backward. 
It is covered by the parotid gland, and by the integument. 

The Sphenomandibular Ligament {ligamentum sphenomandibulare; internal lateral 
ligament) (Fig. 310). — The sphenomandibular ligament is a flat, thin band which is 
attached above to the spina angularis of the sphenoid bone, and, becoming broader 
as it descends, is fixed to the lingula of the mandibular foramen. Its lateral surface 
is in relation, above, with the Pterygoideus externus; lower down, it is separated 
from the neck of the condyle by the internal maxillary vessels; still lower, the 
inferior alveolar vessels and nerve and a lobule of the parotid gland lie between 
it and the ramus of the mandible. Its medial surface is in relation with the Ptery- 
goideus internus. 



298 



SYNDESMOLOGY 



The Articular Disk (discus articularis; interarticnlar fihrocartilage ; articular menis- 
cus) (Fig. 311). — The articular disk is a thin, oval plate, placed between the 
condyle of the mandible and the mandibular fossa. Its upper surface is concavo- 
convex from before backward, to accommodate itself to the form of the man- 
dibular fossa and the articular tubercle. Its under surface, in contact with the 
condyle, is concave. Its circumference is connected to the articular capsule; and in 
front to the tendon of the Pterygoideus externus. It is thicker at its periphery, 
especially behind, than at its center. The fibers of which it is composed have a 
concentric arrangement, more apparent at the circumference than at the center. 
It divides the joint into two cavities, each of which is furnished with a synovial 
membrane. 







Fig. 310. — Articulation of the mandible. Medial aspect. 



Fig. 



311. — Sagittal section of the articulation of the 
mandible. 



The Synovial Membranes. — The synovial membranes, two in number, are placed one above, 
and the other below, the articular disk. The upper one, the larger and looser of the two, is 
continued from the margin of the cartilage covering the mandibular fossa and articular tubercle 
on to the upper surface of the disk. The lower one passes from the under surface of the disk 
to the neck of the condyle, being prolonged a little farther downward behind than in front. The 
articular disk is sometimes perforated in its center, and the two cavities then communicate with 
each other. 

The Stylomandibular Ligament {ligamentum stylomandibular e) ; stylomaxillary 
ligament (Fig. 310). — The stylomandibular ligament is a specialized band of the 
cervical fascia, which extends from near the apex of the styloid process of the 
temporal bone to the angle and posterior border of the ramus of the mandible, 
between the Masseter and Pterygoideus internus. This ligament separates the 
parotid from the submaxillary gland, and from its deep surface some fibers of the 
Styloglossus take origin. Although classed among the ligaments of the temporo- 
mandibular joint, it can only be considered as accessory to it. 

The nerves of the temporomandibular joint are derived from the auriculotemporal and masse- 
teric branches of the mandibular nerve, the arteries from the superficial temporal branch of the 
external carotid. 

Movements. — The movements permitted in this articulation are extensive. Thus, the mandible 
may be depressed or elevated, or carried forward or backward; a slight amount of side-to-side 
movement is also permitted. It must be borne in mind that there are two distinct joints in this 
articulation — one between the condyle and the articular disk, and another between the disk and 
the mandibular fossa. When the mouth is but slightly opened, as during ordinary conversation. 



COSTOVERTEBRAL ARTICULATIONS 299 

the movement is confined to the lower of the two joints. On the other hand, when the mouth 
IS opened more widely, both jomts are concerned in the movement; in the lower joint the move- 
ment is of a hinge-Uke character, the condyle movmg around a transverse axis on the disk, while 
m the upper jomt the movement is of a gUding character, the disk, together with the condyle, 
gUding forward on to the articular tubercle, around an axis which passes through the mandibular 
foramma. These two movements take place simultaneously, the condyle and disk move for- 
ward on the eminence, and at the same time the condyle revolves on the disk. In shutting the 
mouth the reverse action takes place; the disk glides back, carrying the condyle with it, and this 
at the same tune moves-back to its former position. When the mandible is carried horizontally 
forward, as in protruding the lower incisor teeth in front of the upper, the movement takes place 
principally m the upper joint, the disk and the condyle ghding forward on the mandibular fossa 
and articular tubercle. The grinding or chewing movement is produced by one condyle, with 
its disk, ghding alternately forward and backward, while the other condyle moves simultaneously 
in the opposite direction; at the same time the condyle undergoes a vertical rotation on the disk. 
One condyle advances and rotates, the other condyle recedes and rotates, in alternate succession. 
The mandible is depressed by its own weight, assisted by the Platysma, the Digastricus, the 
Mylohyoideus, and the Geniohyoideus. It is elevated by the Masseter, Pterygoideus internus, 
and the anterior part of the Temporalis. It is drawn forward by the simultaneous action of the 
Pterygoidei internus and externus, the superficial fibers of the Masseter and the anterior fibers 
of the Temporalis; and backward by the deep fibers of the Masseter and the posterior fibers of the 
Temporahs. The grinding movement is caused by the alternate action of the Pterygoidei of 
either side. 

V. Costovertebral Articulations (Articulationes Costovertebrales). 

The articulations of the ribs with the vertebral cokimn may be divided into two 
sets, one connecting the heads of the ribs with the bodies of the vertebrae, another 
uniting the necks and tubercles of the ribs with the transverse processes. 

1. Articulations of the Heads of the Ribs {articulationes capitulorum; costocentral 
articulations) (Fig. 312). — These constitute a series of gliding or arthrodial joints, 
and are formed by the articulation of the heads of the typical ribs with the facets 
on the contiguous margins of the bodies of the thoracic vertebrae and with the 
intervertebral fibrocartilages between them ; the first, tenth, eleventh, and twelfth 
ribs each articulate with a single vertebra. The ligaments of the joints are: 

The Articular Capsule. The Radiate. The Interarticular. 

The Articular Capsule (capsula articularis; capsular ligament).- — The articular 
capsule surrounds the joint, being composed of short, strong fibers, connecting 
the head of the rib with the circumference of the articular cavitv formed bv the 
intervertebral fibrocartilage and the adjacent vertebrae. It is most distinct at 
the upper and lower parts of the articulation; some of its upper fibers pass through 
the intervertebral foramen to the back of the intervertebral fibrocartilage, while 
its posterior fibers are continuous with the ligament of the neck of the rib. 

The Radiate Ligament (ligamentum capituli costw radiatum; anterior costoverte- 
bral or stellate ligament). — The radiate ligament connects the anterior part of the 
head of each rib with the side of the bodies of two vertebrae, and the interverte- 
bral fibrocartilage between them. It consists of three flat fasciculi, which are 
attached to the anterior part of the head of the rib, just beyond the articular sur- 
face. The superior fasciculus ascends and is connected with the body of the verte- 
bra above ; the inferior one descends to the body of the vertebra below ; the middle 
one, the smallest and least distinct, is horizontal and is attached to the interver- 
tebral fibrocartilage. The radiate ligament is in relation, in front, w^th the thoracic 
ganglia of the sympathetic trunk, the pleura, and, on the right side, with the azygos 
vein; behind, with the interarticular ligament and synovial membranes. 

In the case of the first rib, this ligament is not divided into three fasciculi, but 
its fibers are attached to the body of the last cervical vertebra, as well as to that 
of the first thoracic. In the articulations of the heads of the tenth, eleventh, and 
twelfth ribs, each of which articulates with a single vertebra, the triradiate arrange- 



T 
\ 



300 



SYNDESMOLOGY 



ment does not exist; but the fibers of the ligament in each case are connected to 
the vertebra above, as well as to that with which the rib articulates. 

The Interarticular Ligament {ligamentum capituli coster interarticulare) .■ — The in- 
terarticular ligament is situated in the interior of the joint. It consists of a short 
band of fibers, flattened from above downward, attached by one extremity to the 
crest separating the two articular facets on the head of the rib, and by the other 
to the intervertebral fibrocartilage ; it divides the joint into two cavities. In the 
joints of the first, tenth, eleventh, and twelfth ribs, the interarticular ligament does 
not exist; consequently, there is but one cavity in each of these articulations. 
This ligament is the homologue of the ligamentum conjugale present in some 
mammals, and uniting the heads of opposite ribs, across the back of the inter- 
vertebral fibrocartilage. 



Anterior 

costotransverse 

ligaments 




i 



Interarticular ligament Intervertebral fibrocartilage 

Fig. 312. — Costovertebral articulations. Anterior view. 

Synovial Membranes. — There are two synovial membranes in each of the articulations where 
an interarticular ligament exists, one above and one below this structure; but only one in those 
joints where there are single cavities. 

2. Costotransverse Articulations {articulationes costotransversaricB) (Fig. ;U3). — 
The articular portion of the tubercle of the rib forms with the articular surface 
on the adjacent transverse process an arthrodial joint. 

In the eleventh and twelfth ribs this articulation is wanting. 

The ligaments of the joint are : 

The Articular Capsule. The Posterior Costotransverse. 

The Anterior Costotransverse. The Ligament of the Neck of the Rib. 

The Ligament of the Tubercle of the Rib. 



COSTOVERTEBRAL ARTICULATIONS 



301 



The Articular Capsule (capsula articularis; capsular ligament). — The articular cap- 
sule is a thin membrane attached to the circumferences of the articular surfaces, 
and lined by a synovial membrane. 



ynovial cavity 




Anterior costotransverse 
ligament divided 

Ligament of the neck 

Ligament of the 
tubercle 



Articular capsule 



Fia. 313. — Costotransverse articulation. Seen from above. 

The Anterior Costotransverse Ligament {liga- 
mentum costotransversarimn anterius; anterior 
superior ligament).- — The anterior costotrans- 
verse ligament is attached below to the sharp 
crest on the upper border of the neck of the 
rib, and passes obliquely upward and lateral- 
ward to the lower border of the transverse 
process immediately above. It is in relation, 
in front, with the intercostal vessels and 
nerves; its medial border is thickened and 
free, and bounds an aperture which transmits 
the posterior branches of the intercostal vessels 
and nerves; its lateral border is continuous 
with a thin aponeurosis, which covers the 
Intercostalis externus. 

The first rib has no anterior costotransverse 
ligament. A band of fibers, the lumbocostal 
ligament, in series with the anterior costotrans- 
verse ligaments, connects the neck of the 
twelfth rib to the base of the transverse pro- 
cess of the first lumbar vertebra; it is merely 
a thickened portion of the posterior layer of 
the lumbodorsal fascia. 

The Posterior Costotransverse Ligament {liga- 
mentum costotransversarium, posterius). ■ — The 
posterior costotransverse ligament is a feeble 
band which is attached below to the neck of 
the rib and passes upward and medialward to the base of the transverse process 
and lateral border of the inferior articular process of the vertebra above. 




Fig. 314. — Seotion of the costotransverse 
joints from the third to the ninth inclusive. 
Contrast the concave facets on the upper with 
the flattened facets on the lower transverse 
processes. 



302 SYNDESMOLOGY 

The Ligament of the Neck of the Rib {ligamentum colli costw; middle costotransverse 
or interosseous ligament). — The ligament of the neck of the rib consists of short 
but strong fibers, connecting the rough surface on the back of the neck of the rib 
with the anterior surface of the adjacent transverse process. A rudimentary 
Hgament may be present in the case of the eleventh and twelfth ribs. 

The Ligament of the Tubercle of the Rib {ligamentum tuberculi costcp; posterior 
costotransverse ligament). — The ligament of the tubercle of the rib is a short but 
thick and strong fasciculus, which passes obliquely from the apex of the transverse 
process to the rough non-articular portion of the tubercle of the rib. The ligaments 
attached to the upper ribs ascend from the transverse processes; they are shorter 
and more oblique than those attached to the inferior ribs, which descend slightly. 

Movements. — The heads of the ribs are so closely connected to the bodies of the vertebrae 
by the radiate and interarticular hgaments that only slight gUding movements of the articular 
surfaces on one another can take place. Similarly, the strong Hgaments binding the necks and 
tubercles of the ribs to the transverse processes limit the movements of the costotransverse 
joints to sUght gliding, the nature of which is determined by the shape and direction of the articular 
surfaces (Fig. 314). In the upper six ribs the articular surfaces on the tubercles are oval in shape 
and convex from above do-«Tiward; they fit into corresponding concavities on the anterior sur- 
faces of the transverse processes, so that upward and downward movements of the tubercles are 
associated with rotation of the rib neck on its long a.xis. In the seventh, eighth, ninth, and tenth 
ribs the articular surfaces on the tubercles are flat, and are directed obliquely downward, medial- 
ward, and backward. The surfaces with which they articulate are placed on the upper margins 
of the transverse processes; when, therefore, the tubercles are drawn up they are at the same 
time carried backward and medialward. The two joints, costocentral and costotransverse, move 
simultaneously and in the same directions, the total effect being that the neck of the rib moves 
as if on a single joint, of which the costocentral and costotransverse articulations form the ends. 
In the upper six ribs the neck of the rib moves but slightly upward and downward; its chief 
movement is one of rotation around its own long axis, rotation backward being associated with 
depression, rotation forward with elevation. In the seventh, eighth, ninth, and tenth ribs the 
neck of the rib moves upward, backward, and medialward, or downward, forward, and lateral- 
ward; very slight rotation accompanies these movements. 

VI. Sternocostal Articulations (Articulationes Sternocostales ; Costosternal 

Articulations) (Fig. 315). 

The articulations of the cartilages of the true ribs with the sternum are 
arthrodial joints, with the exception of the first, in which the cartilage is directly 
united with the sternum, and which is, therefore, a synarthrodial articulation. 
The ligaments connecting them are: 

The Articular Capsules. The Interarticular Sternocostal. 

The Radiate Sternocostal. The Costoxiphoid. 

The Articular Capsules (capsulce articulares; capsular ligaments). — The articular 
capsules surround the joints between the cartilages of the true ribs and the 
sternum. They are very thin, intimately blended with the radiate sternocostal 
ligaments, and strengthened at the upper and lower parts of the articulations by a 
few fibers, which connect the cartilages to the side of the sternum. 

The Radiate Sternocostal Ligaments (ligamenta sternocostalia radiata; chondro- 
sternal or sternocostal ligaments) .■ — These ligaments consist of broad and thin mem- 
branous bands that radiate from the front and back of the sternal ends of the 
cartilages of the true ribs to the anterior and posterior surfaces of the sternum. 
They are composed of fasciculi which pass in different directions. The superior 
fasciculi ascend obliquely, the inferior fasciculi descend obliquely, and the middle 
fasciculi run horizontally. The superficial fibers are the longest; they intermingle 
with the fibers of the ligaments above and below them, with those of the opposite 
side, and in front with the tendinous fibers of origin of the Pectoralis major, form- 



STERNOCOSTAL ARTICULATIONS 



303 



ing a thick fibrous membrane (membrana sterni) which envelopes the sternum. 
This is more distinct at tlie lower than at the upper part of the bone. 

The Interarticular Sternocostal Ligament (ligamentum stcrnocostale interarticularc ; 
interarticular chondr aster mil I ic/ament).— This Hgament is found constantly onlv 
between the second costal cartilages and the sternum. The cartilage of the second 

The synovial cavities are exposed by 
a coronal section of the sternum and cartilages 

Cartilage continuous with 
sternum 



Interarticular ligament and 
two synovial rnembranes 




Single synovial 
membrane 



FiQ. 315. — Sternocostal and interchondral articulations. Anterior view. 



rib is connected with the sternum by means of an interarticular ligament, attached 
by one end to the cartilage of the rib, and by the other to the fibrocartilage which 
unites the manubrium and body of the sternum. This articulation is provided 
with two synovial membranes. Occasionally the cartilage of the third rib is con- 
nected with the first and second pieces of the body of the sternum by an interartic- 
ular ligament. Still more rarely, similar ligaments are found in the other four 



304 SYNDESMOLOGY 

joints of the series. In the lower two the ligament sometimes completely obliterates 
the cavity, so as to convert the articulation into an amphiarthrosis. 

The Costoxiphoid Ligaments {ligamenta costoxiphoidea; chondroxiphoid ligaments). 
— These ligaments connect the anterior and posterior surfaces of the seventh 
costal cartilage, and sometimes those of the sixth, to the front and back of the 
xiphoid process. They vary in length and breadth in different subjects; those on 
the back of the joint are less distinct than those in front. 

Synovial Membranes. — There is no s>Tiovial membrane between the first costal cartilage and 
the sternum, as this cartilage is directly continuous with the manubrium. There are two in the 
articulation of the second costal cartilage and generally one in each of the other joints; but those 
of the sixth and seventh sternocostal joints are sometimes absent; where an interarticular liga- 
ment is present, there are two synovial cavities. After middle life the articular surfaces lose their 
poUsh, become roughened, and the synovial membranes apparently disappear. In old age, the 
cartilages of most of the ribs become continuous with the sternum, and the joint cavities are 
consequently obliterated. 

Movements. — SUght gliding movements are permitted in the sternocostal articulations. 

Interchondral Articulations {articulationes interchondrales; articulations of the 
cartilages of the ribs with each other) (Fig. 315). — ^The contiguous borders of the sixth, 
seventh, and eighth, and sometimes those of the ninth and tenth, costal cartilages 
articulate with each other by small, smooth, oblong facets. Each articulation 
is enclosed in a thin articular capsule, lined by synovial membrane and strengthened 
laterally and medially by ligamentous fibers (interchondral ligaments) which pass 
from one cartilage to the other. Sometimes the fifth costal cartilages, more rarely 
the ninth and tenth, articulate by their lower borders with the adjoining cartilages 
by small oval facets; more frequently the connection is by a few ligamentous fibers. 

Costochondral Articulations. — The lateral end of each costal cartilage is received 
into a depression in the sternal end of the rib, and the two are held together by the 
periosteum. 

Vn. Articulation of the Manubrium and Body of the Sternum. 

The manubrium is imited to the bodv of the sternum either bv an amphiarthrodial 
joint — a piece of fibrocartilage connecting the segments — or by a diarthrodial 
joint, in which the articular surface of each bone is clothed with a lamina of car- 
tilage. In the latter case, the cartilage covering the body is continued without 
interruption on to the cartilages of the facets for the second ribs. Rivington 
found the diarthrodial form of joint in about one-third of the specimens examined 
by him, INIaisonneuve more frequently. It appears to be rare in childhood, and 
is formed, in Rivington's opinion, from the amphiarthrodial form, by absorption. 
The diarthrodial joint seems to have no tendency to ossify, while the amphiar- 
throdial is more liable to do so, and has been found ossified as earlv as thirtv-four 
years of age. The two segments are further connected by anterior and posterior 
interstemal ligaments consisting of longitudinal fibers. 

Mechanism of the Thorax. — Each rib possesses its own range and variety of movements, but 
the movements of all are combined in the respiratory excursions of the thorax. Each rib may 
be regarded as a lever the fulcrum of which is situated immediately outside the costotransverse 
articulation, so that when the body of the rib is elevated the neck is depressed and vice versa; 
from the disproportion in length of the arms of the lever a shght movement at the vertebral end 
of the rib is greatly magnified at the anterior extremity. 

The anterior ends of the ribs he on a lower plane than the posterior; when therefore the body 
of the rib is elevated the anterior extremity is thrust also forward. Again, the middle of the body 
of the rib hes in a plane below that passing through the two extremities, so that when the body 
is elevated relatively to its ends it is at the same time carried outward from the median plane 
of the thorax. Further, each rib forms the segment of a curve which is greater than that of the 
rib immediately above, and therefore the elevation of a rib increases the transverse diameter 
of the thorax in the plane to which it is raised. The modifications of the rib movements at their 
vertebral ends have already been described (page 302). Further modifications result from the 



ARTICULATION OF THE MANUBRIUM AND BODY OF STERNUM 305 



attachments of their anterior extremities, and it is convenient therefore to consider separately 
the movements of the ribs of the three groups— vertebrosternal, vertebrochondral, and vertebral. 

Vertebrosternal Ribs (Figs. 316, 
3 17). — The first rib differs from the 
others of this group in that its at- 
tachment to the sternum is a rigid 
one; this is counterbalanced to some 
extent by the fact that its head 
possesses no interarticular hgament, 
and is therefore more movable. The 
first pair of ribs with the manu- 
brium sterni move as a single piece, 
the anterior portion being elevated 
by rotatory movements at the 
vertebral extremities. In normal 
quiet respiration the movement of 
this arc is practically 7dl; when it 
does occur the anterior part is 
raised and cari'ied forward, increas- 
ing the antero-posterior and trans- 
verse diameters of this region of the 
chest. The movement of the second 
rib is also slight in normal respira- 
tion, as its anterior extremity is 
fixed to the manubrium, and pre- 
vented therefore from moving up- 
ward. The sternocostal articulation, 
however, allows the middle of the 
body of the rib to be drawn up, and 

in this way the transverse thoracic diameter is increased. Elevation of the third, fourth, fifthi 
and sixth ribs raises and thrusts forward their anterior extremities, the greater part of the move- 
ment being effected by the rotation of the rib neck backward. The thrust of the anterior 
extremities carries forward and upward the body of the sternum, which moves on the joint 




c \^V^ 


A 


_\Vv\\ 




1 J'- •' 



Fig. 310. — Lateral view of first and seventh ribs in position, show- 
ing the movements of the sternum and ribs in A, ordinary expiration; 
B, quiet inspiration; C, deep inspiration. 





FiQ. 317. — Diagram showing the axes of movement 
(A B and C D) oi a vertebrosternal rib. The inter- 
rupted lines indicate the position of the rib in 
inspiration. 



Fio. 3l8. — Diagram showing the axis of movement 
(A B) of a vertebrochondral rib. The interrupted Jinea 
indicate the position of the rib in inspiration. 



between it and the manubrium, and thus the antero-posterior thoracic diameter is increased. 
This movement is, however, soon arrested, and the elevating force is then expended in raising 
the middle part of the body of the rib and everting its lower border; at the same time the 
20 



306 SYNDESMOLOGY 

costochondral angle is opened out. By these latter movements a considerable increase in the 
transverse diameter of the thorax is effected. 

Vertebrochondral Ribs (Fig. 318). — The seventh rib is included with this group, as it conforms 
more closely to their type. While the movements of these ribs assist in enlarging the thorax 
for respiratory purposes, they are also concerned in increasing the upper abdominal space for 
viscera displaced by the action of the diaphragm. The costal cartilages articulate with one 
another, so that each pushes up that above it, the final thrust being directed to pushing forward 
and upward the lower end of the body of the sternum. The amount of elevation of the .anterior 
extremities is limited on account of the very slight rotation of the rib neck. Elevation of the 
shaft is accompanied b}'^ an outward and backward movement; the outward movement everts 
the anterior end of the rib and opens up the subcostal angle, while the backward movement 
pulls back the anterior extremity and counteracts the forward thrust due to its elevation; this 
latter is most noticeable in the lower ribs, which are the shortest. The total result is a consider- 
able increase in the transverse and a diminution in the median antero-posterior diameter of the 
upper part of the abdomen; at the same time, however, the lateral antero-posterior diameters of 
the abdomen are increased. 

Vertebral Ribs. — Since these ribs have free anterior extremities and only costocentral articula- 
tions with no interarticular ligaments, they are capable of sUght movements in all directions. 
When the other ribs are elevated these are depressed and fixed to form points of action for the 
diaphragm. 

Vin. Articulation of the Vertebral Column with the Pelvis. 

The ligaments connecting the fifth lumbar vertebra with the sacrum are similar 
to those which join the movable segments of the vertebral column with each other 
— viz.: 1. The continuation downward of the anterior and posterior longitudinal 
ligaments. 2. The intervertebral fibrocartilage, connecting the body of the fifth 
lumbar to that of the first sacral vertebra and forming an amphiarthrodial joint. 
3. Ligamenta flava, uniting the laminae of the fifth lumbar vertebra with those 
of the first sacral. 4. Capsules connecting the articular processes and forming 
a double arthrodia. 5. Inter- and supraspinal ligaments. 

On either side an additional ligament, the iliolumbar, connects the pelvis with 
the vertebral column. 

The Iliolumbar Ligament iligamentum iliolumhale) (Fig. 319). — The iliolumbar 
ligament is attached above to the lower and front part of the transverse process 
of the fifth lumbar vertebra. It radiates as it passes lateralward and is attached 
by two main bands to the pelvis. The lower bands run to the base of the sacrum, 
blending with the anterior sacroiliac ligament; the upper is attached to the crest 
of the ilium immediately in front of the sacroiliac articulation, and is continuous 
above with the lumbodorsal fascia. In front, it is in relation with the Psoas major; 
behind, with the muscles occupying the vertebral groove; above, with the Quadratus 
lumborum. 

DC. Articulations of the Pelvis. 

The ligaments connecting the bones of the pelvis with each other may be divided 
into four groups: 1. Those connecting the sacrum and ilium. 2. Those passing 
between the sacrum and ischium. 3. Those uniting the sacrum and coccyx. 4. 
Those between the two pubic bones. 

1. Sacroiliac Articulation (articulatio sacroiliaca). — The sacroiliac articulation 
is an amphiarthrodial joint, formed between the auricular surfaces of the sacrum 
and the ilium. The articular surface of each bone is covered with a thin plate 
of cartilage, thicker on the sacrum than on the ilium. These cartilaginous plates 
are in close contact with each other, and to a certain extent are united together 
by irregular patches of softer fibrocartilage, and at their upper and posterior part 
by fine interosseous fibers. In a considerable part of their extent, especially in 
advanced life, they are separated by a space containing a synovia-like fluid, and 
hence the joint presents the characteristics of a diarthrosis. The ligaments of the 
joint are: 

The Anterior Sacroiliac. The Posterior Sacroiliac. 

The Interosseous. 



ARTICULATION OF THE PELVIS 



307 



The Anterior Sacroiliac Ligament {ligamentum sacroiliacum anterius) (Fig. 319).— 
The anterior sacroiliac ligament consists of numerous thin bands, which connect 



the anterior surface of the lateral part of the sacrum to the margin of the auricul 
surface ot the ilium and to the preauricular sulcus 



ar 



Anterior sacroiliac lig. 

Iliolumbar ligament Lumbosacral ligament 

/ Anterior longitudinal lig. 




Inguinal ligament^ 



Sacrospinous ligament -f 



Sacrotuberous ligament / 
Fig. 319.- — Articulations ot pelvis. Anterior view. (Quain.) 



Intcrpubic fibrocart. 



The Posterior Sacroiliac Ligament (ligamentum sacroiliacum posterius) (Fig. 320). 
— The posterior sacroiliac ligament is situated in a deep depression between the 
sacrum and ilium behind; it is strong and forms the chief bond of union between 
the bones. It consists of numerous fasciculi, which pass between the bones in 



308 



SYNDESMOLOGY 



various directions. The upper part (short posterior sacroiliac ligament) is nearly 
horizontal in direction, and passes from the first and second transverse tubercles 
on the back of the sacrum to the tuberosity of the ilium. The lower part (long 
posterior sacroiliac ligament) is oblique in direction; it is attached by one extremity 



1 



Iliolumbar ligament 
Supraspinal ligament I 

Short post, sacroiliac lig. \ 



"- -Long post, sacroiliac lig 




Sacrospinous ligament 



Superficial post, sacrococ 
cygeal ligament 



Sacrotuberous ligament 
Fig. 320. — Articulations of pelvis. Posterior view. (Quain ) 

to the third transverse tubercle of the back of the sacrum, and by the other to the 
posterior superior spine of the ilium. 

The Interosseous Sacroiliac Ligament (ligamentum sacroiliacum interosseum) . — ■ 
This ligament lies deep to the posterior ligament, and consists of a series of short, 
strong fibers connecting the tuberosities of the sacrum and ilium. 



ARTICULATIONS OF THE PELVIS 309 

2. Ligaments Connecting the Sacrum and Ischium (Fig. 320). 

The Sacrotuberous. The Sacrospinous. 

The Sacrotuberous Ligament (ligamentum sacrotuherosum; great or posterior 
sacrosciatic ligament) .—lYie sacrotuberous ligament is situated at the lower and 
back part of the pelvis. It is flat, and triangular in form; narrower in the middle 
than at the ends; attached by its broad base to the posterior inferior spine of the 
ilium, to the fourth and fifth transverse tubercles of the sacrum, and to the lower 
part of the lateral margin of that bone and the coccyx. Passing obliquely downward, 
forward, and lateralward, it becomes narrow and thick, but at its insertion into 
the inner margin of the tuberosity of the ischium, it increases in breadth, and is 
prolonged forward along the inner margin of the ramus, as the falciform process, 
the free concave edge of which gives attachment to the obturator fascia; one of its 
surfaces is turned toward the perineum, the other toward the Obturator internus. 
The lower border of the ligament is directly continuous with the tendon of origin 
of the long head of the Biceps femoris, and by many is believed to be the proximal 
end of this tendon, cut off by the projection of the tuberosity of the ischium. 

Relations. — The posterior surface of this ligament gives origin, by its whole extent, to the 
Glutseus maximus. Its anterior surface is in part united to the sacrospinous ligament. Its upper 
border forms, above, the posterior boundary of the greater sciatic foramen, and, below, the pos- 
terior boundary of the lesser sciatic foramen. Its lower border forms part of the boundary of the 
perineum. It is pierced by the coccygeal nerve and the coccygeal branch of the inferior gluteal 
artery. 

The Sacrospinous Ligament {ligamentum sacrospinosum; small or anterior sacro- 
sciatic ligament). — The sacrospinous ligament is thin, and triangular in form; 
it is attached by its apex to the spine of the ischium, and medially, by its broad 
base, to the lateral margins of the sacrum and coccyx, in front of the sacrotuberous 
ligament with which its fibers are intermingled. 

Relations. — It is in relation, anteriorly, with the Coccygeus muscle, to which it is closely con- 
nected; posteriorly, it is covered by the sacrotuberous ligament, and crossed by the internal 
pudendal vessels and nerve. Its upper border forms the lower boimdary of the greater sciatic 
foramen; its lower border, part of the margin of the lesser sciatic foramen. 

These two ligaments convert the sciatic notches into foramina. The greater sciatic foramen 
is bounded, in front and above, by the posterior border of the hip bone; behind, by the sacrotuberous 
ligament;" and below, by the sacrospinous hgament. It is partially filled up, in the recent state, 
by the Piriformis which leaves the pelvis through it. Above this muscle, the superior gluteal 
vessels and nerve emerge from the pelvis; and below it, the inferior gluteal vessels and nerve, 
the internal pudendal vessels and nerve, the sciatic and posterior femoral cutaneous nerves, and 
the nerves to the Obturator internus and Quadratus femoris make their exit from the pelvis. 
The lesser sciatic foramen is bounded, in front, by the tuberosity of the ischium; above, by the 
spine of the ischium and sacrospinous ligament; behind, by the sacrotuberous hgament. It trans- 
mits the tendon of the Obturator internus, its nerve, and the internal pudendal vessels and nerve. 

3. Sacrococcygeal Symphysis {symphysis sacrococcygea; articulation of the sacrum 
and coccyx). — This articulation is an amphiarthrodial joint, formed between the 
oval surface at the apex of the sacrum, and the base of the coccyx. It is homol- 
ogous with the joints between the bodies of the vertebrae, and is connected by 
similar ligaments. They are: 

The Anterior Sacrococcygeal. The Lateral Sacrococcygeal. 

The Posterior Sacrococcygeal. The Interposed Fibrocartilage. 

The Interarticular. 

The Anterior Sacrococcygeal Ligament {ligamentum sacrococcygeum anterius). — 
This consists of a few irregular fibers, which descend from the anterior surface 
of the sacrum to the front of the coccyx, blending with the periosteum. 

The Posterior Sacrococcygeal Ligament {ligamentum sacrococcygeum posterius). — 
This is a flat band, which arises from the margin of the lower orifice of the sacral 



310 SYNDESMOLOGY 

canal, and descends to be inserted into the posterior surface of the coccyx. This 
ligament completes the lower and back part of the sacral canal, and is divisible 
into a short deep portion and a longer superficial part. It is in relation, behind, 
with the Gluta^us maximus. 

The Lateral Sacrococcygeal Ligament {ligamentum sacrococcygeum laterale; inter- 
transverse ligament). — The lateral sacrococcygeal ligament exists on either side 
and connects the transverse process of the coccyx to the lower lateral angle of the 
sacrum; it completes the foramen for the fifth sacral nerve. 

A disk of fibrocartilage is interposed between the contiguous surfaces of the 
sacrum and coccyx; it differs from those between the bodies of the vertebrae in 
that it is thinner, and its central part is firmer in texture. It is somewhat thicker 
in front and behind than at the sides. Occasionally the coccjtc is freely movable 
on the sacrum, most notably during pregnancy ; in such cases a synovial membrane 
is present. 

The Interarticular Ligaments are thin bands, which unite the cornua of the two 
bones. 

The different segments of the coccyx are connected together by the extension 
downward of the anterior and posterior sacrococcygeal ligaments, thin annular 
disks of fibrocartilage being interposed between the segments. In the adult male, 
all the pieces become ossified together at a comparatively early period ; but in the 
female, this does not commonly occur until a later period of life. At more advanced 
age the joint between the sacrum and coccyx is obliterated. 

Movements. — The movements which take place between the sacrum and coccyx, and between 
the different pieces of the latter bone, are forward and backward; they are very limited. Their 
extent increases during pregnancy. 

4. The Pubic Symphysis {symphysis ossium pubis; articulation of the pubic 
bones) (Fig. 321). — The articulation between the pubic bones is an amphiarthro- 
dial joint, formed between the two oval articular surfaces of the bones. The 
ligaments of this articulation are: 

The Anterior Pubic. The Superior Pubic. 

The Posterior Pubic. • The Arcuate Pubic. 

The Interpubic Fibrocartilaginous Lamina. 

The Anterior Pubic Ligament (Fig. 319). — The anterior pubic ligament consists 
of several superimposed layers, which pass across the front of the articulation. 
The superficial fibers pass obliquely from one bone to the other, decussating and 
forming an interlacement with the fibers of the aponeuroses of the Obliqui externi 
and the medial tendons of origin of the Recti abdominis. The deep fibers pass 
transversely across the symphysis, and are blended with the fibrocartilaginous 
lamina. 

The Posterior Pubic Ligament. — The posterior pubic ligament consists of a few 
thin, scattered fibers, which unite the two pubic bones posteriorly. 

The Superior Pubic Ligament (ligamentum pubicum superius). — The superior 
pubic ligament connects together the two pubic bones superiorly, extending later- 
ally as far as the pubic tubercles. 

The Arcuate Pubic Ligament {ligamentum arcuatum pubis; inferior pubic or 
subpubic ligament). — The arcuate pubic ligament is a thick, triangular arch of 
ligamentous fibers, connecting together the two pubic bones below, and forming 
the upper boundary of the pubic arch. Above, it is blended with the interpubic 
fibrocartilaginous lamina; laterally, it is attached to the inferior rami of the 
pubic bones; below, it is free, and is separated from the fascia of the urogenital 
diaphragm by an opening through which the deep dorsal vein of the penis passes 
into the pelvis. 



ARTICULATIONS OF THE PELVIS 



311 



The Interpubic Fibrocartilaginous Lamina {lamina fibrocartilaginea interpubica; 
inter pubic disk). —The interpubic fibrocartilaginous lamina connects the opposed 
surfaces of the pubic bones. Each of these surfaces is covered by a thin layer of 
hyaline cartilage firmly joined to the bone by a series of nipple-like processes which 
accurately fit into corresponding depressions on the osseous surfaces. These 
opposed cartilaginous surfaces are connected together by an intermediate lamina 
of fibrocartilage which varies in thickness in different subjects. It often contains 
a cavity in its interior, probably formed by the softening and absorption of the 
fibrocartilage, since it rarely appears before the tenth year of life and is not lined 
by synovial membrane. This cavity is larger in the female than in the male, but 
it is very doubtful whether it enlarges, as was formerly supposed, during pregnancy. 
It is most frequently limited to the upper and back part of the joint; it occasion- 
ally reaches to the front, and may extend the entire length of the cartilage. It may 
be easily demonstrated when present by making a coronal section of the symphysis 
pubis near its posterior surface (Fig. 321). 



Ant. sup. iliac spine- 



Obturator canal 
Lacunar ligament 
Pubic tubercle \ 



Interpubic 
fibro- _. 
cartilagiiioiis 
lamina 




ansverse acetabular 
ligament 



Fig. 321. — Symphysis pubis exposed by a coronal section. 



Mechanism of the Pelvis. — The pelvic girdle supports and protects the contained viscera and 
affords surfaces for the attachments of the trunk and lower limb muscles. Its most important 
mechanical function, however, is to transmit the weight of the trunk and upper limbs to the 
lower extremities. 

It may be divided into two arches by a vertical plane passing through the acetabular cavities; 
the posterior of these arches is the one chiefly concerned in the fimction of transmitting the 
weight. Its essential parts are the upper three sacral vertebrae and two strong pillars of bone 
running from the sacroihac articulations to the acetabular cavities. For the reception and diffu- 
sion of the weight each acetabular cavity is strengthened by two additional bars running toward 
the pubis and ischium. In order to lessen concussion in rapid changes of distribution of the 
weight, joints (sacroiliac articulations) are interposed between the sacrum and the ihac bones; 
an accessory joint (pubic symphysis) exists in the middle of the anterior arch. The sacrum forms 
the summit of the posterior arch; the weight transmitted faUs on it at the lumbosacral articula- 
tion and, theoretically, has a component in each of two directions. One component of the force 
is expended in driving the sacrum downward and backward between the ihac bones, while the 
other thrusts the upper end of the sacrum downward and forward toward the pelvic cavity. 



312 



SYXDESMOLOGY 



The movements of the sacrum are regulated by its form. Viewed as a whole, it presents the 
shape of a wedge with its base upward and forward. The first component of the force is there- 













Fig. 322. — Coronal section of anterior sacral segment. 

fore acting against the resistance of the wedge, and its tendency to separate the iUac bones is 
resisted by the sacroiliac and iliolumbar ligaments and by the ligaments of the pubic sj'mphysis. 




Fia. 323. — Coronal section of middle sacra segment 

If a series of coronal sections of the sacroiliac joints be made, it will be found possible to cfivide 
the articular portion of the sacrum into three segments: anterior, middle, and posterior. In 
the anterior segment (Fig. 322), which involves the first sacral vertebra, the articular surfaces 

show slight sinuosities and are almost parallel 
to one another; the distance between their 
dorsal margins is, however, slightly greater 
than that between their ventral marginsr- 
This segment therefore presents a sUght 
wedge shape with the truncated apex down- 
ward. The middle segment (Fig. 323) is a 
narrowband across the centers of the articu- 
lations. Its dorsal width is distinctly 
greater than its ventral, so that the segment 
is more definitely wedge-shaped, the trun- 
cated apex being again directed downward. 
Each articular surface presents in the center 
a marked concavity from above downward, 
and into this a corresponding convexity of the ihac articular surface fits, forming an interlocking 
mechanism. In the posterior segment (Fig. 324) the ventral width is greater than the dorsal, 
so that the wedge form is the reverse of those of the other segments — i. e., the truncated apex 
is directed upward. The articular surfaces are only shghtly concave. 

Dislocation downward and forward of the sacrum by the second component of the force applied 
to it is prevented therefore by the middle segment, which interposes the resistance of its wedge 




Fig. 324. — Coronal section of posterior sacral segment. 



STERNOCLAVICULAR ARTICULATION 313 

shape and that of the interlocking mechanism on its surfaces; a rotatory movement, however, 
is produced by which the anterior segment is tilted downward and the posterior upward; the axis 
of this rotation passes through the dorsal part of the middle segment. The movement of the 
anterior segment is slightly limited by its wedge form, but chiefly by the posterior and inter- 
osseous sacroiliac ligaments; that of the posterior segment is checked to a slight extent by its 
wedge form, but the chief limiting factors are the sacrotuberous and sacrospinous ligaments. 
In all these movements the efifect of the sacroiliac and iholumbar ligaments and the ligaments 
of the symphysis pubis in resisting the separation of the ihac bones must be recognized. 

During pregnancy the pelvic joints and hgaments are relaxed, and capable therefore of more 
extensive movements. When the fetus is being expelled the force is applied to the front of the 
sacrum. Upward dislocation is again prevented by the interlocking mechanism of the middle 
segment. As the fetal head passes the anterior segment the latter is carried upward, enlarging 
the antero-posterior diameter of the pelvic inlet; when the head reaches the posterior segment 
this also is pressed upward against the resistance of its wedge, the movement only being possible 
by the laxity of the joints and the stretching of the sacrotuberous and sacrospinous ligaments. 

ARTICULATIONS OF THE UPPER EXTREMITY. 

The articulations of the Upper Extremity may be arranged as follows: 

I. Sternoclavicular. VI. Wrist. 

II. Acromioclavicular. VII. Intercarpal. 

III, Shoulder. VIII. Carpometacarpal. 

IV. Elbow. IX. Intermetacarpal. 

V. Radioulnar. X. INIetacarpophalangeal. 

XL Articulations of the Digits. 

I. Sternoclavicular Articulation (Articulatio Sternoclavicularis) (Fig. 325). 

The sternoclavicular articulation is a double arthrodial joint. The parts entering 
into its formation are the sternal end of the clavicle, the upper and lateral part 
of the manubrium sterni, and the cartilage of the first rib. The articular surface 
of the clavicle is much larger than that of the sternum, and is invested with a layer 
of cartilage,^ which is considerably thicker than that on the latter bone. The 
ligaments of this joint are: 

The Articular Capsule. The Interclavicular. 

The Anterior Sternoclavicular. The Costoclavicular. 

The Posterior Sternoclavicular. The Articular Disk. 

The Articular Capsule (capsula articiilaris; capsular ligament). — The articular 
capsule surrounds the articulation and varies in thickness and strength. In front 
and behind it is of considerable thickness, and forms the anterior and posterior 
sternoclavicular ligaments; but above, and especially below, it is thin and par- 
takes more of the character of areolar than of true fibrous tissue. 

The Anterior Sternoclavicular Ligament {ligamentum sternoclavicular e anterior). — 
The anterior sternoclavicular ligament is a broad band of fibers, covering the 
anterior surface of the articulation; it is attached above to the upper and front part 
of the sternal end of the clavicle, and, passing obliquely downward and medialward, 
is attached below to the front of the upper part of the manubrium sterni. This 
ligament is covered by the sternal portion of the Sternocleidomastoideus and the 
integument; behind, it is in relation with the capsule, the articular disk, and the 
two synovial membranes. 

The Posterior Sternoclavicular Ligament {ligamentum sternoclaviculare posterius) . — 
The posterior sternoclavicular ligament is a similar band of fibers, covering the 
posterior surface of the articulation ; it is attached above to the upper and back 

' According to Bruch, the sternal end of the clavicle is covered by a tissue which is fibrous rather than cartilaginous 
in structure. 



314 



SYNDESMOLOGY 



part of the sternal end of the clavicle, and, passing obliquely downward and 
medialward, is fixed below to the back of the upper part of the manubrium sterni. 
It is in relation, in fro7it, wuth the articular disk and synovial membranes; behind, 
with the Sternohyoideus and Sternothyreoideus. 

The Interclavicular Ligament (ligamentum interclaviculare) .■ — This ligament is a 
flattened band, which varies considerably in form and size in different individuals, 
it passes in a curved direction from the upper part of the sternal end of one clavicle 
to that of the other, and is also attached to the upper margin of the sternum. It 
is in relation, in front, with, the integurtient and Sternocleidomastoidei ; behind, 
with the Sternothyreoidei. 

The Costoclavicular Ligament {ligamentum costoclavicular e; rhomboid ligament). — 
This ligament is short, fiat, strong, and rhomboid in form. Attached below to 
the upper and medial part of the cartilage of the first rib, it ascends obliquely 
backward and lateralward, and is fixed above to the costal tuberosity on the under 
surface of the clavicle. It is in relation, in front, with the tendon of origin of the 
Subclavius; behind, with the subclavian vein. 




Fig. 325. ^Sternoclavicular articulation. An terior view. 



The Articular Disk {discus articularis) . — The articular disk is flat and nearly 
circular, interposed between the articulating surfaces of the sternum and clavicle. 
It is attached, above, to the upper and posterior border of the articular surface of 
the clavicle ; beloiv, to the cartilage of the first rib, near its junction with the sternum ; 
and by its circumference to the interclavicular and anterior and posterior sterno- 
clavicular ligaments. It is thicker at the circumference, especially its upper and 
back part, than at its center. It divides the joint into two cavities, each of which 
is furnished with a synovial membrane. 

Synovial Membranes. — Of the two synovial membranes found in this articulation, the lateral 
is reflected from the sternal end of the clavicle, over the adjacent surface of the articular disk, 
and around the margin of the facet on the cartilage of the first rib; the medial is attached to the 
margin of the articular surface of the sternum and clothes the adjacent surface of the articular 
disk ; the latter is the larger of the two. 

Movements. — This articulation admits of a limited amount of motion in nearly every direc- 
tion — upward, downward, backward, forward, as well as circumduction. When these move- 
ments take place in the joint, the clavicle in its motion carries the scapula with it, this bone 
gliding on the outer surface of the chest. This joint therefore forms the center from which all 
movements of the supporting arch of the shoulder originate, and is the only point of articulation 
of the shoulder girdle with the trunk. The movements attendant on elevation and depression of 
the shoulder take place between the clavicle and the articular disk, the bone rotating upon the 
ligament on an axis drawn from before backward through its own articular facet; when the shoulder 
is moved forward and backward, the clavicle, with the articular disk rolls to and fro on the 



ACROMIOCLAVICULAR ARTICULATION 315 

articular surface of the sternum, revolving, with a shding movement, around an axis drawn nearly 
vertically through the sternum; in the circumduction of the shoulder, which is compounded of 
these two movements, the clavicle revolves upon the articular disk and the latter, with the clavicle, 
rolls upon the sternum.* Elevation of the shoulder is hmited principally by the costoclavicular 
ligament; depression, by the interclavicular hgament and articular disk. The muscles which 
raise the shoulder are the upper fibers of the Trapezius, the Levator scapula, and the clavicular 
head of the Sternocleidomastoideus, assisted to a certain extent by the lihomboidci, which pull 
the vertebral border of the scapula backward and upward and so raise the shoulder. The depres- 
sion of the shoulder is principally effected by gravity assisted by the Subclavius, Pectoralis minor 
and lower fibers of the Trapezius. The shoulder is drawn backward by the Rhomboidei and the 
middle and lower fibers of the Trapezius, and forward by the Serratus anterior and Pectoralis 
minor. 

II. Acromioclavicular Articulation (Articulatio Acromioclavicularis ; Scapulo- 
clavicular Articulation) (Fig. 326). 

The acromioclavicular articulation, is an arthrodial joint between the acromial 
end of the clavicle and the medial margin of the acromion of the scapula. Its 
ligaments are: 

The Articular Capsule. The Articular Disk. 

The Superior Acromioclavicular. m. /-^ i • i (Trapezoid and 

The Inferior Acromioclavicular. ^he Coracoclavicular \ ^^^^jj 

The Articular Capsule {cajjsula articularis; capsular ligament). — The articular 
capsule completely surrounds the articular margins, and is strengthened above 
and below by the superior and inferior acromioclavicular ligaments. 

The Superior Acromioclavicular Ligament (ligamentuni acromioclaviculare) . — 
This ligament is a quadrilateral band, covering the superior part of the articula- 
tion, and extending between the upper part of the acromial end of the clavicle 
and the adjoining part of the upper surface of the acromion. It is composed 
of parallel fibers, which interlace with the aponeuroses of the Trapezius and 
Deltoideus; helow, it is in contact M'ith the articular disk when this is present. 

The Inferior Acromioclavicular Ligament. — This ligament is somewhat thinner 
than the preceding; it covers the under part of the articulation, and is attached to 
the adjoining surfaces of the two bones. It is in relation, above, in rare cases with 
the articular disk; below, with the tendon of the Supraspinatus. 

The Articular Disk (discus articularis). — The articular disk is frequently absent 
in this articulation. When present, it generally only partially separates the artic- 
ular surfaces, and occupies the upper part of the articulation. More rarely, it 
completely divides the joint into two cavities. 

The Synovial Membrane. — There is usually only one synovial membrane in this articulation, 
but when a complete articular disk is present, there are two. 

The Coracoclavicular Ligament {ligamentuni coracoclaviculare) (Fig. 326). — This 
ligament serves to connect the clavicle with the coracoid process of the scapula. 
It does not properly belong to this articulation, but is usually described with it, 
since it forms a most efficient means of retaining the clavicle in contact with the 
acromion. It consists of two fasciculi, called the trapezoid and conoid ligaments. 

The Trapezoid Ligament iligamentum trapezoideum) , the anterior and lateral fas- 
ciculus, is broad, thin, and quadrilateral: it is placed obliquely between the cora- 
coid process and the clavicle. It is attached, below, to the upper surface of the 
coracoid process; above, to the oblique ridge on the under surface of the clavicle. 
Its anterior border is free; its posterior border is joined with the conoid ligament, 
t'he two forming, by their junction, an angle projecting backward. 

The Conoid Ligament (ligamentum conoideum), the posterior and medial fasciculus, 
is a dense band of fibers, conical in form, with its base directed upward. It is 

1 Humphry, On the Human Skeleton, page 402. 



316 



SYNDESMOLOGY 



attached by its apex to a rough impression at the base of the coracoid process, 
medial to the trapezoid Hgament; above, by its expanded base, to the coracoid 
tuberosity on the under surface of the clavicle, and to a line proceeding medial- 
ward from it for 1.25 cm. These ligaments are in relation, in front, with the 
Subclavius and Deltoideus; behind, with the Trapezius. 




Fio. 326. — The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula. 

Movements. — ^The movements of this articulation are of two kinds: (1) a gliding motion of 
the articular end of the clavicle on the acromion; (2) rotation of the scapula forward and back- 
ward upon the clavicle. The extent of this rotation is limited by the two portions of the coraco- 
clavicular hgament, the trapezoid limiting rotation forward, and the^ conoid backward. 

The acromioclavicular joint has important functions in the movements of the upper extremity. 
It has been well pointed out by Humphry, that if there had been no joint between the clavicle 
and scapula, the circular movement of the scapula on the ribs (as in throwing the shoulders back- 
ward or forward) would have been attended with a greater alteration in the direction of the 
shoulder than is consistent with the free use of the arm in such positions, and it would have been 
impossible to give a blow straight forward with the full force of the arm; that is to say, with the 
combined force cf the scapula, arm, and forearm. "This joint," as he happily says, "is so adjusted 
as to enable either bone to turn in a hinge-hke manner upon a vertical axis drawn through the 
other, and it permits the surfaces of the scapula, like the baskets in a roundabout swing, to look 
the same way in every position, or nearly so." Again, when the whole arch formed by the clavicle 
and scapula rises and falls (in elevation or depression of the shoulder), the joint between these 
two bones enables the scapula still to maintain its lower part in contact with the ribs. 



THE LIGAMENTS OF THE SCAPULA. 

The ligaments of the scapula (Fig. 32G) are: 

Coracoacromial, Superior and Inferior Transverse. 

The Coracoacromial Ligament {ligamentum coracoacromiale) .■ — This ligament is a 
strong triangular band, extending between the coracoid process and the acromion. 



HUMERAL ARTICULATION OR SHOULDER-JOINT 317 

It is attached, by its apex, to the summit of the acromion just in front of the 
articular surface for the clavicle; and by its broad base to the whole length of the 
lateral border of the coracoid process. This ligament, together with the coracoid 
process and the acromion, forms a vault for the protection of the head of the 
humerus. It is in relation, above, with the clavicle and under surface of the Del- 
toideus; hehw, with the tendon of the Supraspinatus, a bursa being interposed. 
Its lateral border is continuous with a dense lamina that passes beneath the Del- 
toideus upon the tendons of the Supraspinatus and Infraspinatus. The ligament 
is sometimes described as consisting of two marginal bands and a thinner inter- 
vening portion, the two bands being attached respectively to the apex and the 
base of the coracoid process, and joining together at the acromion. When the 
Pectoralis minor is inserted, as occasionally is the case, into the capsule of the 
shoulder-joint instead of into the coracoid process, it passes between these two 
bands, and the intervening portion of the ligament is then deficient. 

The Superior Transverse Ligament {ligamentum transversum scapulcp superius; 
transverse or suprascapular ligament) .—This ligament converts the scapular notch 
into a foramen. It is a thin and flat fasciculus, narrower at the middle than at the 
extremities, attached by one end to the base of the coracoid process, and by the 
other to the medial end of the scapular notch. The suprascapular nerve runs 
through the foramen; the transverse scapular vessels cross over the ligament. 
The ligament is sometimes ossified. 

The Inferior Transverse Ligament (ligamentum transversum scapula' inferius; 
spinoglenoid ligament). — This ligament is a weak membranous band, situated 
behind the neck of the scapula and stretching from the lateral border of the spine 
to the margin of the glenoid cavity. It forms an arch under which the transverse 
scapular vessels and suprascapular nerve enter the infraspinatous fossa. 

III. Humeral Articulation or Shoulder- joint (Articulatio Humeri) (Fig. 326). 

The shoulder-joint is an enarthrodial or ball-and-socket joint. The bones 
entering into its formation are the hemispherical head of the humerus and the 
shallow glenoid cavity of the scapula, an arrangement which permits of very 
considerable movement, while the joint itself is protected against displacement 
by the tendons which surround it. The ligaments do not maintain the joint sur- 
faces in apposition, because when they alone remain the humerus can be separated 
to a considerable extent from the glenoid cavity; their use, therefore, is to limit 
the amount of movement. The joint is protected above by an arch, formed by 
the coracoid process, the acromion, and the coracoacromial ligament. The artic- 
ular cartilage on the head of the humerus is thicker at the center than at the cir- 
cumference, the reverse being the case with the articular cartilage of the glenoid 
cavity. The ligaments of the shoulder are: 

The Articular Capsule. The Glenohumeral. 

The Coracohumeral. The Transverse Humeral. 

The Glenoidal Labrum.^ 

The Articular Capsule {capsula articularis; capsular ligament) (Fig. 327) .^The 
articular capsule completely encircles the joint, being attached, above, to the 
circumference of the glenoid cavity beyond the glenoidal labrum; below, to the 
anatomical neck of the humerus, approaching nearer to the articular cartilage 
above than in the rest of its extent. It is thicker above and below than elsewhere, 
and is so remarkably loose and lax, that it has no action in keeping the bones in 
contact, but allows them to be separated from each other more than 2.5 cm., an 

' The long tendon of origin of the biceps brachii also acts as one of the hgaments of this joint. See the observations 
on page 287, on the function of the muscles passing over more than one joint. 



318' 



SYNDESMOLOGY 



evident provision for that extreme freedom of movement which is peculiar to this 
articulation. It is strengthened, above, by the Supraspinatus; beloic, by the long 
head of the Triceps brachii; behind, by the tendons of the Infraspinatus and Teres 
minor; and in front, by the tendon of the Subscapularis. There are usually three 
openings in the capsule. One anteriorly, below the coracoid process, establishes 
a communication between the joint and a bursa beneath the tendon of the Sub- 
scapularis. The second, which is not constant, is at the posterior part, where an 
opening sometimes exists between the joint and a bursal sac under the tendon 
of the Infraspinatus. The third is between the tubercles of the humerus, for the 
passage of the long tendon of the Biceps brachii. 

The Coracohumeral Ligament {ligamentum coracohumerale) .- — This ligament is 
a broad band which strengthens the upper part of the capsule. It arises from 
the lateral border of the coracoid process, and passes obliquely downward and 
lateralward to the front of the greater tubercle of the humerus, blending with the 



Superior transverse ligament 



Transverse 
humeral 
ligament 

Prolongation of 

synovial mem- 

brane on tendon 

of Biceps brachii 




Bursa 

U)ider 
Subscapularis 



Fig. 327. — Capsule of shoulder-joint (distended), .\nterior aspect. 



tendon of the Supraspinatus. This ligament is intimately united to the capsule 
by its hinder and lower border; but its anterior and upper border presents a free 
edge, which overlaps the capsule. 

Glenohumeral Ligaments, — In addition to the coracohumeral ligament, three 
supplemental l)ands, which are named the glenohumeral ligaments, strengthen 
the capsule. These may be best seen by opening the capsule at the back of the 
joint and removing the head of the humerus. One on the medial side of the joint 
passes from the medial edge of the glenoid cavity to the lower part of the lesser 
tubercle of the humerus. A second at the lower part of the* joint extends from 
the under edge of the glenoid cavity to the under part of the anatomical neck of 
the humerus. A third at the upper part of the joint is fixed above to the apex 
of the glenoid cavity close to the root of the coracoid process, and passing down- 
ward along the medial edge of the tendon of the Biceps brachii, is attached below 
to a small depression above the lesser tubercle of the humerus. In addition to 



HUMERAL ARTICULATION OR SHOULDER-JOINT 



319 



CONOID LIGAMENT 



RACOID 
OCESS 



these, the capsule is strengthened in front by two bands derived from the tendons 
of the Pectoralis major and Teres major respectively. 

The Transverse Humeral Ligament (Fig. 327) is a broad band passing from the 
lesser to the greater tubercle of the humerus, and always limited to that portion 
of the bone which lies above the epiphysial line. It converts the intertubercular 
groove into a canal, and is the homologue of the strong process of bone which 
connects the summits of the two tubercles in the musk ox. 

The Glenoidal Labrum {labrium glenoidale: glenoid ligavient) is a fibrocartihaginous 
rim attached around the margin of the glenoid cavity. It is triangular on section, 
the base being fixed to the circumference of the cavity, while the free edge is thin 
and sharp. It is continuous above with the tendon of the long head of the Biceps 
brachii, which gives off two fasciculi to blend with the fibrous tissue of the labrum. 
It deepens the articular cavity, and protects the edges of the bone. 

Synovial Membrane. — The synovial membrane is reflected from the margin of the glenoid 
cavity over the labrum; it is then reflected over the inner surface of the capsule, and covers 
the lower part and sides of the anatomical neck of the 
humerus as far as the articular cartilage on the head of 
the bone. The tendon of the long head of the Biceps 
brachii passes through the capsule and is enclosed in a 
tubular sheath of synovial membrane, which is reflected 
upon it from the summit of the glenoid cavity and is 
continued around the tendon into the intertubercular 
groove as far as the surgical neck of the humerus (Fig. 
327). The tendon thus traverses the articulation, but it 
is not contained within the synovial cavity. 

Bursse. — The bursa3 in the neighborhood of the 
shoulder-joint are the following: (1) A constant bursa 
is situated between the tendon of the Subscapularis 
muscle and the capsule; it communicates with the 
synovial cavity through an opening in the front of the 
capsule; (2) a bursa which occasionally communicates 
with the joint is sometimes found between the tendon 
of the Infraspinatus and the capsule; (3) a large bursa 
exists between the under surface of the Deltoideus and 
the capsule, but does not communicate with the joint; 
thi.« bursa is prolonged under the acromion and coraco- 

acromial ligament, and intervenes between these structures and the capsule; (4) a large bursa 
is situated on the summit of the acromion; (5) a bursa is frequently found between the cora- 
coid process and the capsule; (6) a bursa exists beneath the Coracobrachialis; (7) one lies 
between the Teres major and the long head of the Triceps brachii; (8) one is placed in front of, 
and another behind, the tendon of the Latissimus dorsi. 

The muscles in relation with the joint are, above, the Supraspinatus; below, the long head of 
the Triceps brachii; in front, the Subscapularis; behind, the Infraspinatus and Teres minor; luithin, 
the tendon of the long head of the Biceps brachii. The Deltoideus covers the articulation in 
front, behind, and laterally. 

The arteries supplying the joint are articular branches of the anterior and posterior humeral 
circumflex, and transverse scapular. 

The nerves are derived from the axillary and suprascapular. 

Movements. — The shoulder-joint is capable of every variety of movement, flexion, extension, 
abduction, adduction, circumduction, and rotation. The humerus is flexed (drawn forward) 
by the Pectorahs major, anterior fibers of the Deltoideus, Coracobrachialis, and when the fore- 
arm is flexed, by the Biceps brachii; extended (drawn backward) by the Latissimus dorsi, Teres 
major, posterior fibers of the Deltoideus, and, when the forearm is extended, by the Triceps 
brachii; it is abducted by the Deltoideus and Supraspinatus; it is adducted by the Subscapularis, 
Pectorahs major, Latissimus dorsi, and Teres major, and by the weight of the hmb; it is rotated 
outward by the Infraspinatus and Teres minor; and it is rotated inward by the SuKscapularis, 
Latissimus dorsi. Teres major, Pectorahs major, and the anterior fibers of the Deltoideus. 

The most striking pecuharities in this joint are: (1) The large size of the head of the humerus 
in comparison with the depth of the glenoid cavity, even when this latter is supplemented by the 
glenoidal labrum. (2) The looseness of the capsule of the joint. (3) The intimate connection of 
the capsule with the muscles attached to the head of the humerus. (4) The pecuhar relation of 
the tendon of the long head of the Biceps brachii to the joint. 




Fig. 328. — Glenoid fossa of right side. 



320 SYNDESMOLOGY 

It is in consequence of the relative sizes of the two articular surfaces, and the looseness of 
the articular capsule, that the joint enjoys such free movement in all directions. When these 
movements of the arm are arrested in the shoulder-joint by the contact of the bony surfaces, 
and by the tension of the fibers of the capsule, together with that of the muscles acting as accessory 
ligaments, the arm can be carried considc-ably farther by the movements of the scapula, involv- 
ing, of coui'se, motion at the acromio- and sternoclavicular joints. These joints are therefore 
to be regarded as accessory structures to the shoulder-joint (see pages 314 and 316). The extent 
of the scapular movements is very considerable, especially in extreme elevation of the arm, a 
movement best accomplished when the arm is thrown somewhat forward and outward, because 
the margin of the head of the humerus is by no means a true circle; its greatest diameter is from 
the intertubercular groove, downward, medialward, and backward, and the greatest elevation 
of the arm can be obtained by rolling its articular surface in the direction of this measurement. 
The great width of the central portion of the humeral head also allows of very free horizontal 
movement when the arm is raised to a right angle, in which movement the arch formed by the 
acromion, the coracoid process and the coracoacromial ligament, constitutes a sort of supple- 
mental articular cavity for the head of the bone. 

The looseness of the capsule is so great that the arm will fall about 2.5 cm. from the scapula 
when the muscles are dissected from the capsule, and an opening made in it to counteract the 
atmospheric pressure. The movements of the joint, therefore, are not regulated by the capsule 
so much as by the surrounding muscles and by the pressure of the atmosphere, an arrangement 
which "renders the jnovements of the joint much more easy than they would otherwise have 
been, and permits a swinging, pendulum-Uke vibration of the limb when the muscles are at rest" 
(Humphry). The fact, also, that in all ordinary positions of the joint the capsule is not put on 
the stretch, enables the arm to move freely in all directions. Extreme movements are checked 
by the tension of appropriate portions of the capsule, as well as by the interlocking of the bones. 
Thus it is said that "abduction is checked by the contact of the great tuberosity with the upper 
edge of the glenoid cavity; adduction by the tension of the coracohumeral ligament" (Beaunis 
et Bouchard). Cleland' maintains that the limitations of movement at the shoulder-joint are 
due to the structure of the joint itself, the glenoidal labrum fitting, in different positions of the 
elevated arm, into the anatomical neck of the humerus. 

The scapula is capable of being moved upward and downward, forward and backward, or, by 
a combination of these movements, circumducted on the wall of the chest. The muscles which 
raise the scapula are the upper fibers of the Trapezius, the Levator scapula-, and the Rhomboidei; 
those which depress it are the lower fibers of the Trapezius, the Pectoralis minor, and, through 
the clavicle, the Subclavius. The scapula is drawn backward by the Rhomboidei and the middle 
and lower fibers of the Trapezius, and forward by the Serratus anterior and Pectoralis minor, 
assisted, when the arm is fixed, by the Pectoralis major. The mobility of the scapula is very 
considerable, and greatly assists the movements of the arm at the shoulder-joint. Thus, in 
raising the arm from the side, the Deltoideus and Supraspinatus can only lift it to a right angle 
with the trunk, the further elevation of the limb being effected by the Trapezius and Serratus 
anterior moving the scapula on the wall of the chest. This mobihty is of special importance in 
ankylosis of the shoulder-joint, the movements of this bone compensating to a very great extent 
for the immobility of the joint. 

Cathcart- has pointed out that in abducting the arm and raising it above the head, the scapula 
rotates throughout the whole movement with the exception of a short space at the beginning 
and at the end; that the humerus moves on the scapula not only while passing from the hanging 
to the horizontal position, but also in travelling upward as it approaches the vertical above; 
that the clavicle moves not only during the second half of the movement but in the first as well, 
though to a less extent — i. e., the scapula and clavicle are concerned in the first stage as well 
as in the second; and that the humerus is partly involved in the second as well as chiefly in the 
first. 

The intimate union of the tendons of the Supraspinatus, Infraspinatus, Teres minor and 
Subscapularis with the capsule, converts these muscles into elastic and spontaneously acting 
ligaments of the joint. 

The peculiar relations of the tendon of the long head of the Biceps brachii to the shoulder- 
joint appear to subserve various purposes. In the first place, by its connection with both the 
shoulder and elbow the muscle harmonizes the action of the two joints, and acts as an elastic 
ligament in all positions, in the manner previously discussed (see page 287). It strengthens the 
upper part of the articular cavity, and prevents the head of the humerus from being pressed up 
against the acromion, when the Deltoideus contracts; it thus fixes the head of the humerus as 
the center of motion in the glenoid cavity. By its passage along the intertubercular groove it 
assists in steadying the head of the humerus in the various movements of the arm. When the 
arm is raised from the side it assists the Supraspinatus and Infraspinatus in rotating the head 
of the humerus in the glenoid cavity. It also holds the head of the bone firmly in contact with 
the glenoid cavity, and prevents its slipping over its lower edge, or being displaced by the action 
of the Latissimus dorsi and Pectoralis major, as in climbing and many other movements. 

' Journal of Anatomy and Physiology, 1S67, i, 85. ^Ibid., 1SS4, vol. xviii. 



ELBOW-JOINT 



321 



IV. 



Elbow-joint (Articulatio Cubiti) (Pigs. 



329, 330). 

The elbow-joint is a ginglymus or hinge-joint. The trochlea of the humerus is 
received into the semilunar notch of the ulna, and the capitulum of the humerus 
articulates with the fovea on the head of the radius. The articular surfaces are 
connected together by a capsule, which is thickened medially and laterally, and, 
to a less extent, in front and behind. These thickened portions are usually described 
as distinct ligaments under the following names : 

The Anterior. The Ulnar Collateral. 

The Posterior. The Radial Collateral. 





FiQ. 329. — Left elbow-joint, showing anterior and 
ulnar collateral ligaments. 



FiQ. 330. — Left elbow-joint, showing posterior and 
radial collateral ligaments. 



The Anterior Ligament (Fig. 329).- — The anterior ligament is a broad and thin 
fibrous layer covering the anterior surface of the joint. It is attached to the front 
of the medial epicondyle and to the front of the humerus immediately above the 
coronoid and radial fossae; below, to the anterior surface of the coronoid process 
of the ulna and to the annular ligament (page 324), being continuous on either 
side with the collateral ligaments. Its superficial fibers pass obliquely from the 
medial epicondyle of the humerus to the annular ligament. The middle fibers, 
vertical in direction, pass from the upper part of the coronoid depression and 
become partly blended with the preceding, but are inserted mainly into the anterior 
surface of the coronoid process. The deep or transverse set intersects these at 
right angles. This ligament is in relation, in front, with the Brachialis, except 
at its most lateral part. 
21 



322 SYNDESMOLOGY 

The Posterior Ligament (Fig. 330). — This posterior ligament is thin and mem- 
branous, and consists of transverse and oblique fibers. Above, it is attached to 
the humerus* immediately behind the capitulum and close to the medial margin 
of the trochlea, to the margins of the olecranon fossa, and to the back of the lateral 
epicondyle some little distance from the trochlea. Below, it is fixed to the upper 
and lateral margins of the olecranon, to the posterior part of the annular ligament, 
and to the ulna behind the radial notch. The transverse fibers form a strong band 
which bridges across the olecranon fossa; under cover of this band a pouch of 
synovial membrane and a pad of fat project into the upper part of the fossa when 
the joint is extended. In the fat are a few scattered fibrous bundles, which pass 
from the deep surface of the transverse band to the upper part of the fossa. This 
ligament is in relation, behind, with the tendon of the Triceps brachii and the 
Ancona?us. 

The Ulnar Collateral Ligament (ligamentum collaterale ulnare; internal lateral 
ligament) (Fig. 329). — This ligament is a thick triangular band consisting of two 
portions, an anterior and posterior united by a thinner intermediate portion. The 
anterior portion, directed obliquely forward, is attached, above, by its apex, to the 
front part of the medial epicondyle of the humerus; and, below, by its broad base 
to the medial margin of the coronoid process. The posterior portion, also of trian- 
gular form, is attached, above, by its apex, to the lower and back part of the medial 
epicondyle; below, to the medial margin of the olecranon. Between these two 
bands a few intermediate fibers descend from the medial epicondyle to blend with 
a transverse band which bridges across the notch between the olecranon and the 
coronoid process. This ligament is in relation with the Triceps brachii and Flexor 
carpi ulnaris and the ulnar nerve, and gives origin to part of the Flexor digitorum 
sublimis. 

The Radial Collateral Ligament (ligamentum collaterale radiale; external lateral 
ligament) (Fig. 330). — This ligament is a short and narrow fibrous band, less dis- 
tinct than the ulnar collateral, attached, above, to a depression below the lateral 
epicondyle of the humerus; below, to the annular ligament, some of its most pos- 
terior fibers passing over that ligament, to be inserted into the lateral margin of 
the ulna. It is intimately blended with the tendon of origin of the Supinator. 

Synovial Membrane (Figs. 331, 332). — The synovial membrane is very extensive. It extends 
from the margin of the articular surface of the humerus, and lines the coronoid, radial and olec- 
ranon"fossse on that bone; it is reflected over the deep surface of the capsule and forms a pouch 
between the radial notch, the deep surface of the annular ligament, and the circumference of the 
head of the radius. Projecting between the radius and ulna into the cavity is a crescentic fold of 
synovial membrane, suggesting the division of the joint into two; one the humeroradial, the 
other the humeroulnar. 

Between the capsule and the synovial membrane are three masses of fat: the largest, over 
the olecranon fossa, is pressed into the fossa by the Triceps brachii during the flexion ; the second, 
over the coronoid fossa, and the third, over the radial fossa, are pressed by the Brachialis into 
their respective fossae during extension. 

The muscles in relation with the joint are, in front, the Brachialis; behind, the Triceps brachii 
and Anconams; laterally, the Supinator, and the common tendon of origin of the Extensor muscles; 
medially, the common tendon of origin of the Flexor muscles, and the Flexor carpi ulnaris. 

The arteries supplying the joint are derived from the anastomosis between the profunda and 
the superior and inferior ulnar collateral branches of the brachial, with the anterior, posterior, 
and interosseous recurrent branches of the uhiar, and the recurrent branch of the radial. These 
vessels form a complete anastomotic network around the joint. 

The nerves of the joint are a twig from the ulnar, as it passes between the medial condyle and 
the olecranon; a filament from the musculocutaneous, and two from the median. 

Movements.— The elbow-joint comprises three different portions — viz., the joint between 
the ulna and humerus, that between the head of the radius and the humerus, and the proximal 
radioulnar articulation, described below. All these articular surfaces are enveloped by a common 
synovial membrane, and the movements of the whole joint should be studied together. The com- 
bination of the movements of flexion and extension of the forearm with those of pronation and 
supination of the hand, which is ensured by the two being performed at the same joint, is essential 
to the accm-acy of the various minute movements of the hand. 



ELBOW-JOINT 



323 



The portion of the joint between the ulna and humerus is a simple hinge-joint, and allows of 
movements of flexion and extension only. Owing to the obliquity of the trochlea of the humerus, 
this movement does not take place in the antero-posterior plane of the body of the humerus. 
When the forearm is extended and supinated, the axes of the arm and forearm are not in the same 
Une; the arm forms an obtuse angle with the forearm, the hand and forearm being directed lateral- 
ward. During flexion, however, the forearm and the hand tend to approach the middle line of 
the body, and thus enable the hand to be easily carried to the face. The accurate adaptation 
of the trochlea of the humerus, with its prominences and depressions, to the semilunar notch of 
the uhia, prevents any lateral movement. Flexion is produced by the action of the Biceps brachii 
and Brachialis, assisted by the Brachioradialis and the muscles arismg from the medial condyle 
of the humerus; extension, by the Triceps brachii and Ancona;us, assisted by the Extensors of 
the wrist, the Extensor digitorum communis, and the Extensor digiti quinti proprius. 





Fig. 331. — Capsule of elbow-joint (distended). 
Anterior aspect. 



FiQ. 332. — Capsule of elbow-joint (distended). 
Posterior aspect. 



The joint between the head of the radius and the capitulum of the humerus is an arthrodial 
joint. The bony surfaces would of themselves constitute an enarthrosis and allow of movement 
in all directions, were it not for the annular ligament, by which the head of the radius is bound 
to the radial notch of the ulna, and which prevents any separation of the two bones laterally. 
It is to the same ligament that the head of the radius owes its security from dislocation, which 
would otherwise tend to occur, from the shallowness of the cup-like surface on the head of the 
radius. In fact, but for this ligament, the tendon of the Biceps brachii would be hable to pull 
the head of the radius out of the joint. The head of the radius is not in complete contact with 
the capitulum of the humerus in all positions of the joint. The capitulum occupies only the 
anterior and inferior surfaces of the lower end of the humerus, so that in complete extension a 
part of the radial head can be plainly felt projecting at the back of the articulation. In full 
flexion the movement of the radial head is hampered by the compression of the surrounding soft 
parts, so that the freest rotatory movement of the radius on the humerus (pronation and supina- 
tion) takes place in semiflexion, in which position the two articular surfaces are in most intimate 



324 



SYNDESMOLOGY 



contact. Flexion and extension of the elbow-joint are limited by the tension of the structures 
on the front and back of the joint; the limitation of flexion is also aided by the soft structures of 
the arm and forearm coming into contact. 

In any position of flexion or extension, the radius, carrying the hand with it, can be rotated in 
the proximal radioulnar joint. The hand is directly articulated to the lower surface of the radius 
only, and the ulnar notch on the lower end of the radius travels around the lower end of the ulna. 
The latter bone is excluded from the wrist -joint by the articular disk. Thus, rotation of the head 
of the radius aroimd an axis passing through the center of the radial head of the humerus imparts 
circular movement to the hand through a very considerable arc. 



V. Radioulnar Articulations (Articulatio Radioulnaris). 

The articulation of the radius with the ulna is effected by ligaments which con- 
nect together the extremities as well as the bodies of these bones. The ligaments 
may, consequently, be subdivided into three sets: 1, those of the proximal radio- 
ulnar articulation; 2, the middle radioulnar ligaments; 3, those of the distal radio- 
ulnar articulation. 

Proximal Radioulnar Articulation {articulatio radioulnaris proximalis; superior 
radioulnar joint). — This articulation is a trochoid or pivot-joint between the 
circumference of the head of the radius and the ring formed by the radial notch 
of the ulna and the a?mular ligament. 



Head of radius Quadrate Semilunar 

(cut) ligament notch 




Annular ligament 

Radial notch 



Fig. 333.- 



Olecranon {cut) 

-Annular ligament of radius, from above. The head of the radius has been sawn off and the bone 

dislodged from the ligament. 



The Annular Ligament {ligamentum annulare radii; orbicular ligament) (Fig. 333). 
— This ligament is a strong band of fibers, which encircles the head of the radius, 
and retains it in contact with the radial notch of the ulna. It forms about four- 
fifths of the osseo-fibrous ring, and is attached to the anterior and posterior margins 
of the radial notch; a few of its lower fibers are continued around below the cavitv 
and form at this level a complete fibrous ring. Its upper border blends with the 
anterior and posterior ligaments of the elbow, while from its lower border a thin 
loose membrane passes to be attached to the neck of the radius; a thickened band 
which extends from the inferior border of the annular ligament below the radial 
notch to the neck of the radius is known as the quadrate ligament. The superficial 
surface of the annular ligament is strengthened by the radial collateral ligament 
of the elbow, and affords origin to part of the Supinator. Its deep surface is smooth, 
and lined by synovial membrane, which is continuous with that of the elbow-joint. 



RADIOULNAR ARTICULATIONS 325 

Movements.— The movements allowed in this articulation are limited to rotatory movements 
of the head of the radius within the ring formed by the annular ligament and the radial notch 
of the ulna; rotation forward being called pronation; rotation backward, supination. Supination 
is performed by the Biceps brachii and Supinator, assisted to a shght extent by the Extensor 
muscles of the thumb. Pronation is performed by the Pronator teres and Pronator quadratus. 

Middle Radioulnar Union.— The shafts of the radius and uhia are connected 
by the Oblique Cord and the Interosseous Membrane. 

The Oblique Cord {chorda obliqua; oblique ligament) (Fig. 829). — The oblique 
cord is a small, flattened band, extending downward and lateralward, from the 
lateral side of the tubercle of the ulna at the base of the coronoid process to the 
radius a little below the radial tuberosity. Its fibers run in the opposite direction 
to those of the interosseous membrane. It is sometimes wantins:. 

The Interosseous Membrane {memhrana interossea antebrachii). — ^The interosseous 
membrane is a broad and thin plane of fibrous tissue descending obliquely down- 
ward and medialward, from the interosseous crest of the radius to that of the ulna; 
the lower part of the membrane is attached to the posterior of the two lines into 
which the interosseous crest of the radius divides. It is deficient above, commencing 
about 2.5 cm. beneath the tuberosity of the radius; is broader in the middle than 
at either end; and presents an oval aperture a little above its lower margin for the 
passage of the volar interosseous vessels to the back of the forearm. This mem- 
brane serves to connect the bones, and to increase the extent of surface for the 
attachment of the deep muscles. Between its upper border and the oblique cord 
is a gap, through which the dorsal interosseous vessels pass. Two or three fibrous 
bands are occasionallv found on the dorsal surface of this membrane; thev descend 
obliquely from the idna toward the radius, and have consequently a direction 
contrary to that of the other fibers. The membrane is in relation, in front, by 
its upper three-fourths, with the Flexor pollicis longus on the radial side, and with 
the Flexor digitorum profundus on the ulnar, lying in the interval between which 
are the volar interosseous vessels and nerve; by its lower fourth with the Pronator 
quadratus; behind, with the Supinator, Abductor pollicis longus. Extensor pollicis 
brevis. Extensor pollicis longus. Extensor indicis proprius; and, near the wrist, 
with the volar interosseous artery and dorsal interosseous nerve. 

Distal Radioulnar Articulation {articulatio radioulnaris distalis; inferior radio- 
ulnar joint). — This is a pivot-joint formed between the head of the ulna and the 
ulnar notch on the lower end of the radius. The articular surfaces are connected 
together by the following ligaments: 

The Volar Radioulnar. The Dorsal Radioulnar. 

The Articular Disk. 

The Volar Radioulnar Ligament {anterior radioulnar ligament) (Fig. 334). — This 
ligament is a narrow band of fibers extending from the anterior margin of the ulnar 
notch of the radius to the front of the head of the ulna. 

The Dorsal Radioulnar Ligament {posterior radioulnar ligament) (Fig. 335). — 
This ligament extends between corresponding surfaces on the dorsal aspect of the 
articulation. 

The Articular Disk {discus articularis; triangular fibrocariilage) (Fig. 336).— The 
articular disk is triangular in shape, and is placed transversely beneath the head 
of the ulna, binding the lower ends of the ulna and radius firmly together. Its 
periphery is thicker than its center, which is occasionally perforated. It is attached 
by its apex to a depression between the styloid process and the head of the ulna; 
and by its base, which is thin, to the prominent edge of the radius, which separates 
the ulnar notch from the carpal articular surface. Its margins are united to the 
ligaments of the wrist-joint. Its upper surface, smooth and concave, articulates 
with the head of the ulna, forming an arthrodial joint; its under surface, also con- 



326 



SYXDESMOLOGY 



cave and smooth, forms part of the wrist-joint and articulates with the triangular 
bone and medial part of the lunate. Both surfaces are clothed by synovial mem- 
brane; the upper, by that of the distal radioulnar articulation, the under, by that 
of the wrist. 



Distal radio-ulnar 
articulation 




' * " ^^^ " / if-^'^^'Wi ^ ntercarpal art tcvlat ions 

Pisohamate hgarrve^it 

Pisometacarpal ligament 

Carpometacarpal 
nrticidatioiis 



Fig. 334. — Ligaments of wrist. Anterior view 

Synovial Membrane (Fig. 336). — The synovial membrane of this articulation is extremely 
loose, and extends upward as a recess {recessus sacciformis) between the radius and the ulna. 




Distal radio-ulnar, 
articulation 

Wrist-joint 



Iniercarpal articulations 



Carpometacarpal ,«j,: 
articulations 



Fig. 335. — Ligaments of wrist. Posterior \new. 

Movements. — The movements in the distal radioulnar articulation consist of rotation of the 
lower end of the radius around an axis which passes through the center of the head of the ulna. 
When the radius rotates forward, pronation of the forearm and hand is the result; and when back- 
ward, supination. It will thus be seen that in pronation and supination the radius describes the 



RADIOCARPAL ARTICULATION OR WRIST-JOINT 



327 



segment of a cone, the axis of which extends from the center of the head of the radius to the 
middle of the head of the uhia. In this movement tlie head of the ulna is not stationary, but 
describes a curve in a direction opposite to that taken by the head of the radius. This, however, 
is not to be regarded as a rotation of the ulna— the curve which the liead of this bone describes 
is due to a combined antero-posterior and rotatory movement, the former taking place almost 
entirely at the elbow-joint, the latter at the shoulder-joint. , 



Wrist- joint - 



Radial collateral 
ligament 




> J '-' '' 






Pisiform 




Distal radioulnar 
articulation 

Articular disc 

Ulnar collateral ligament 



Fig. 336. — \ertical section through the articulatioas at the wrist, showing the synovial cavities. 



.VI. Radiocarpal Articulation or Wrist-joint (Articulatio Radiocarpea) 

(Figs. 334, 335). 

The wTist-joint is a condyloid articulation. The parts forming it are the lower 
end of the radius and under surface of the articular disk above; and the navicular, 
lunate, and triangular bones below. The articular surface of the radius and the 
under surface of the articular disk form together a transversely elliptical concave 
surface, the receiving cavity. The superior articular surfaces of the navicular, 
lunate, and triangidar form a smooth con^'ex surface, the condyle, which is received 
into the concavity. The joint is surrounded by a capsule, strengthened by the 
following ligaments: 



The Volar Radiocarpal. 
The Dorsal Radiocarpal. 



The Ulnar Collateral. 
The Radial Collateral. 



The Volar Radiocarpal Ligament (ligamentum radiocarpeum volare; anterior liga- 
ment) (Fig. 334). — This ligament is a broad membranous band, attached above 
to the anterior margin of the lower end of the radius, to its styloid process, and to 
the front of the lower end of the ulna; its fibers pass downward and medialward 
to be inserted into the volar surfaces of the navicular, lunate, and triangular 
bones, some being continued to the capitate. In addition to this broad mem- 
brane, there is a rounded fasciculus, superficial to the rest, which reaches from the 
base of the styloid process of the ulna to the lunate and triangular bones. The 
ligament is perforated by apertures for the passage of vessels, anj is in relation, 
in front, with the tendons of the Flexor digitorum profundus and Flexor pollicis 



328 SYNDESMOLOGY 

longus; behind, it is closely adherent to the anterior border of the articular disk 
of the distal radioulnar articulation. 

The Dorsal Radiocarpal Ligament {ligamentum radiocarpeum dorsale; posterior 
ligament) (Fig. 335). — The dorsal radiocarpal ligament less thick and strong than 
the volar, is attached, above, to the posterior border of the lower end of the radius; 
its fibers are directed obliquely downward and medialward, and are fixed, below, 
to the dorsal surfaces of the navicular, lunate, and triangular, being continuous 
with those of the dorsal intercarpal ligaments. It is in relation, behind, with the 
Extensor tendons of the fingers; \n front, it is blended with the articular disk. 

The , Ulnar Collateral Ligament {ligamentum coUaterale carpi idnare; internal 
lateral ligament) (Fig. 334). — The ulnar collateral ligament is a rounded cord, 
attached above to the end of the styloid process of the ulna, and dividing below 
into two fasciculi, one of which is attached to the medial side of the triangular 
bone, the other to the pisiform and transverse carpal ligament. 

The Radial Collateral Ligament {ligamentum coUaterale carpi radiale; external 
lateral ligament) (Fig. 335). — The radial collateral ligament extends from the tip 
of the styloid process of the radius to the radial side of the navicular, some of its 
fibers being prolonged to the greater multangular bone and the transverse carpal 
ligament. It is in relation with the radial artery, which separates the ligament 
from the tendons of the Abductor pollicis longus and Extensor pollicis brevis. 

Synovial Membrane (Fig. 330). — The synovial membrane lines the deep surfaces of the hga- 
ments above described, extending from the margin of the lower end of the radius and articular 
disk above to the margins of the articular surfaces of the carpal bones below. It is loose and 
lax, and presents numerous folds, especially behind. 

The wrist-joint is covered in front by the Flexor, and behind by the Extensor tendons. 

The arteries supplying the joint are the volar and dorsal carpal branches of the radial and 
ulnar, the volar and dorsal metacarpals, and some ascending branches from the deep volar arch. 

The nerves are derived from the ulnar and dorsal interosseous. 

Movements. — The movements permitted in this joint are flexion, extension, abduction, adduc- 
tion, and circumduction. They will be studied with those of the carpus, with which they are 
combined. 

Vn. Intercarpal Articulations (Articulationes Intercarpeae ; Articulations 

of the Carpus). 

These articulations may be subdivided into three sets: 

1. The Articulations of the Proximal Row of Carpal Bones. 

2. The Articulations of the Distal Row of Carpal Bones. 

3. The Articulations of the Two Rows with each Other. 

Articulations of the Proximal Row of Carpal Bones. — These are arthrodial 
joints. The navicular, lunate, and triangular are connected by dorsal, volar, and 
interosseous ligaments. 

The Dorsal Ligaments {ligamenta intercarpea dorsalia) .—The dorsal ligaments, 
two in number, are placed transversely behind the bones of the first row; they 
connect the navicular and lunate, and the lunate and triangular. 

The Volar ligaments {ligamenta intercarpea volaria; palmar ligaments). — The volar 
ligaments, also two, connect the navicular and lunate, and the lunate and trian- 
gular; they are less strong than the dorsal, and placed very deeply behind the 
Flexor tendons and the volar radiocarpal ligament. 

The Interosseous Ligaments {ligamenta intercarpea interossea) (Fig. 336). — The 
interosseous ligaments are two narrow bundles, one connecting the lunate with 
the navicular, the other joining it to the triangular. They are on a level with the 
superior surfaces of these bones, and their upper surfaces are smooth, and form 
part of the convex articular surface of the wrist-joint. 



INTERCARPAL ARTICULATIONS 329 

The ligaments connecting the pisiform bone are the articular capsule and the 
two volar ligaments. 

The articular capsule is a thin membrane which connects the pisiform to the 
triangular; it is lined by synovial membrane. 

The two volar ligaments are strong fibrous bands; one, the pisohamate ligament, 
connects the pisiform to the hamate, the other, the pisometacarpal ligament, joins 
the pisiform to the base of the fifth metacarpal bone (Fig. l^'M). These ligaments 
are, in reality, prolongations of the tendon of the Flexor carpi ulnaris. 

Articulations of the Distal Row of Carpal Bones.— These also are arthrodial 
joints; the bones are connected by dorsal, volar, and interosseous ligaments. • 

The Dorsal Ligaments (ligamenta intercarpea dorsalia). — The dorsal ligaments, 
three in number, extend transversely from one bone to another on the dorsal 
surface, connecting the greater with the lesser multangular, the lesser multangular 
with the capitate, and the capitate with the hamate. 

The Volar Ligaments {ligamenta intercarpea volaria; palmar ligaments). — The 
volar ligaments, also three, have a similar arrangement on the volar surface. 

The Interosseous Ligaments {ligamienta intercarpea interossea). — The three inter- 
osseous ligaments are much thicker than those of the first row; one is placed be- 
tween the capitate and the hamate, a second betw^een the capitate and the lesser 
multangular, and a third between the greater and lesser multangulars. The first 
is much the strongest, and the third is sometimes wanting. 

Articulations of the Two Rows of Carpal Bones with Each Other. — The joint 
between the navicular, lunate, and triangular on the one hand, and the second 
row of carpal bones on the other, is named the midcarpal joint, and is made up of 
three distinct portions: in the center the head of the capitate and the superior 
surface of the hamate articulate with the deep cup-shaped cavity formed by the 
navicular and lunate, and constitute a sort of ball-and-socket joint. On the 
radial side the greater and lesser multangulars articulate with the navicular, and 
on the ulnar side the hamate articulates with the triangular, forming gliding joints. 

The ligaments are: volar, dorsal, ulnar and radial collateral. 

The Volar Ligaments {ligamenta intercarpea volaria; anterior or palmar ligaments) . 
— The volar ligaments consist of short fibers, which pass, for the most part, from 
the volar surfaces of the bones of the first row to the front of the capitate. 

The Dorsal Ligaments {ligamenta intercarpea dorsalia; posterior ligaments). — 
The dorsal ligaments consist of short, irregular bundles passing between the dorsal 
surfaces of the bones of the first and second rows. 

The Collateral Ligaments {lateral ligaments). — The collateral ligaments are very 
short; one is placed on the radial, the other on the ulnar side of the carpus; the 
former, the stronger and more distinct, connects the navicular and greater mul- 
tangular, the latter the triangular and hamate; they are continuous with the 
collateral ligaments of the wrist-joint. In addition to these ligaments, a slender 
interosseous band sometimes connects the capitate and the navicular. 

Synovial Membrane. — The synovial membrane of the carpus is very extensive (Fig. 336), 
and bounds a synovial cavity of very irregular shape. The upper portion of the cavity inter- 
venes between the under surfaces of the navicular, lunate, and triangular bones and the upper 
surfaces of the bones of the second row. It sends two prolongations upward — between the navic- 
ular and lunate, and the lunate and triangular— and three prolongations downward between 
the four bones of the second row. The prolongation between the greater and lesser multangulars, 
or that between the lesser multangular and capitate, is, owing to the absence of the interosseous 
Ugament, often continuous with the cavity of the carpometacarpal joints, sometimes of the 
second, third, fourth, and fifth metacarpal bones, sometimes of the second and third only. In 
the latter condition the joint between the hamate and the fourth and fifth metacarpal bones 
has a separate sjoiovial membrane. The synovial cavities of these joints are prolonged for a 
short distance between the bases of the metacarpal bones. There is a separate synovial mem- 
brane between the pisiform and triangular. 



330 SYNDESMOLOGY 

Movements. — The articulation of the hand and wi-ist considered as a whole involves four 
articular surfaces: (a) the inferior surfaces of the radius and articular disk; (b) the superior 
surfaces of the navicular, lunate, and triangular, the pisiform having no essential part in the 
movement of the hand; (c) the S-shaped surface formed by the inferior suifaces of the navicular, 
lunate, and triangular; {d) the reciprocal surface formed by the upper surfaces of the bones of 
the second row. These four surfaces form two joints: (1) a proximal, the wrist-joint proper; 
and (2) a distal, the mid-carpal joint. 

1. The wTist-joint proper is a true condyloid articulation, and therefore all movements but 
rotation are permitted. Flexion and extension are the most free, and of these a greater amoxmt 
of extension than of flexion is permitted, since the articulating surfaces extend farther on the dorsal 
than on the volar surfaces of the carpal bones. In tliis movement the carpal bones rotate on a 
transv«rse axis drawn between the tips of the stj'loid processes of the radius and ulna. A certain 
amount of adduction (or ulnar flexion) and abduction (or radial flexion) is also permitted. The 
former is considerably greater in extent than the latter on accomit of the shortness of the styloid 
process of the ulna, abduction being soon limited by the contact of the styloid process of the 
radius with the greater multangular. In this movement the carpus revolves upon an antero- 
posterior axis drawn through the center of the WTist.^ Finallj', circumduction is permitted by 
the combined and consecutive movements of adduction, extension, abduction, and flexion. No 
rotation is possible, but the effect of rotation is obtained bj- the pronation and supination of the 
radius on the ulna. • The movement oi flexion is performed by the Flexor carpi radialis, the Flexor 
carpi ulnaris, and the Palmaris longus; extension by the Extensores carpi radiales longus and 
brevis and the Extensor carpi ulnaris; adduction (ulnar flexion) by the Flexor carpi ulnaris and 
the Extensor carpi ulnaris; and abduction (radial flexion) by the Abductor polhcis longus, the 
Extensors of the thumb, and the Extensores carpi radiales longus and brevis and the Flexor carpi 
radiahs. When the fingers are extended, flexion of the wrist is performed by the Flexores carpi 
radialis and uhiaris and extension is aided by the Extensor digitorum communis. When the 
fingers are flexed, flexion of the wrist is aided by the Flexores digitorum sublimis and profundus, 
and extension is performed by the Extensores carpi radiales and uhiaris. 

2. The chief movements permitted in the mid-carpal joint are flexion and extension and a 
slight amount of rotation. In flexion ajid extension, which are the movements most freely enjoj'ed, 
the greater and lesser multangulars on the radial side and the hamate on the ulnar side glide 
forward and backward on the navicular and triangular respectively, while the head of the capitate 
and the superior surface of the hamate rotate in the cup-shaped cavity of the navicular and 
lunate. Flexion at this joint is freer than extension. A very trifling amount of rotation is also 
permitted, the head of the capitate rotating around a vertical axis drawn through its own center, 
while at the same time a shght ghding movement takes place in the lateral and medial portions 
of the joint. 

Vni. Carpometacarpal Articulations (Articulationes Carpometacarpeae). 

Carpometacarpal Articulation of the Thumb {articulatio carpometacarpea poUicis). 
— This is a joint of reciprocal reception between the first metacarpal and the 
greater multangular; it enjoys great freedom of movement on accoimt of the 
configuration of its articular surfaces, which are saddle-shaped. The joint is sur- 
rounded by a capsule, which is thick but loose, and passes from the circumference 
of the base of the metacarpal bone to the rough edge bounding the articular surface 
of the greater multangular; it is thickest laterally and dorsally, and is lined by 
synovial membrane. 

Movements. — In this articulation the movements permitted are flexion and extension in the 
plane of the palm of the hand, abduction and adduction in a plane at right angles to the palm, 
circumduction, and opposition. It is by the movement of opposition that the tip of the thumb 
i3 brought into contact with the volar surfaces of the slightly flexed fingers. This movement is 
effected through the medium of a small sloping facet on the anterior Hp of the saddle-shaped 
articular surface of the greater multangular. The Flexor muscles pull the corresponding part 
of the articular surface of the metacarpal bone on to this facet, and the movement of opposition 
is then carried out by the Adductors. 

Flexion of this joint is produced by the Flexores polhcis longus and brevis, assisted by the 
Opponens poUicis and the Adductor poUicis. Extension is effected mainly by the abductor 
pollicis longus, assisted by the Extensores poUicis longus and brevis. Adduction is carried out 
by the Adductor; abduction mainly by the Abductores poUicis longus and brevis, assisted by the 
Extensors. 

' H. M. Johnston (Journal of Anatomy and Physiology, vol. xli) maintains that n ulnar and radial flexion only 
slight lateral movement occurs at the radiocarpal joint, and that in coinplete flexion and extension of the hand there 
is a small degree of ulnar flexion at the radiocarpal joint. 



INTERMETACARPAL ARTICULATIONS 331 

Articulations of the Other Four Metacarpal Bones with the Carpus (articulationes 
car pometacar pea). —The joints between the carpus and the second, third, fourth, 
and fifth metacarpal bones are arthrodial. The bones are united by dorsal, volar, 
and interosseous ligaments. 

The Dorsal Ligaments (ligamenta carpometacarpea dorsalia). — The dorsal ligaments, 
the strongest and most distinct, connect the carpal and metacarpal bones on their 
dorsal surfaces. The second metacarpal bone receives two fasciculi, one from the 
greater, the other from the lesser multangular; the third metacarpal receives two, 
one each from the lesser multangular and capitate; the fourth two, one each from 
the capitate and hamate; the fifth receives a single fasciculus from the hamate, 
and this is continuous with a similar ligament on the volar surface, forming an 
incomplete capsule. 

• The Volar Ligaments {ligamenta carpometacarpea volaria; palmar ligaments). — 
The volar ligaments have a somewhat similar arrangement, with the exception 
of those of the third metacarpal, which are three in number: a lateral one from the 
greater multangular, situated superficial to the sheath of the tendon of the Flexor 
carpi radialis; and intermediate one from the capitate; and a medial one from 
the hamate. 

The Interosseous Ligaments. — The interosseous ligaments consist of short, thick 
fibers, and are limited to one part of the carpometacarpal articulation; they con- 
nect the contiguous inferior angles of the capitate and hamate with the adjacent 
surfaces of the third and fourth metacarpal bones. 

S3movial Membrane. — The synovial membrane is a continuation of that of the intercarpal 
joints. Occasionally, the joint between the hamate and the fourth and fifth metacarpal bones 
has a separate synovial membrane. 

The synovial membranes of the wrist and carpus (Fig. 3.36) are thus seen to be five in number. 
The first passes from the lower end of the ulnar to the ulnar notch of the radius, and lines the upper 
surface of the articular disk. The second passes from the articular disk and the lower end of the 
radius above, to the bones of the first row below. The third, the most extensive, passes between 
the contiguous margins of the two rows of carpal bones, and sometimes, in the event of one of 
the interosseous ligaments being absent, between the bones of the second row to the carpal extremi- 
ties of the second, third, fourth, and fifth metacarpal bones. The /our//i extends from the margin 
of the greater multangular to the metacarpal bone of the thumb. The fifth runs between the 
adjacent margins of the triangular and pisiform bones. Occasional!}' the fourth and fifth carpo- 
metacarpal joints have a separate synovial membrane. 

Movements. — The movements permitted in the carpometacarpal articulations of the fingers 
are limited to shght gliding of the articular surfaces upon each other, the extent of which varies 
in the different joints. The metacarpal bone of the little finger is most movable, then that of 
the ring finger; the metacarpal bones of the index and middle fingers are almost immovable. 

K. Intermetacarpal Articulations (Articulationes Intermetacarpese ; Articulations 
of the Metacarpal Bones with Each Other). 

The bases of the second, third, fourth and fifth metacarpal bones articulate 
with one another by small surfaces covered with cartilage, and are connected 
together by dorsal, volar, and interosseous ligaments. 

The dorsal {ligamenta basium oss. metacarp. dorsalia) and volar ligam'ents {liga- 
menta hasium oss. metacarp. volaria; palmar ligaments) pass transversely from 
one bone to another on the dorsal and volar surfaces. The interosseous hgaments 
{ligamenta basium oss. metacarp. interossea) connect their contiguous surfaces, 
just distal to their collateral articular facets. 

The synovial membrane for these joints is continuous with that of the carpometacarpal 
articulations. 

The Transverse Metacarpal Ligament {ligamentum capitulorum [oss. metacarpalium] 
transversum) (Fig. 337).— This ligament is a narrow fibrous band, which runs across 
the volar surfaces of the heads of the second, third, fourth and fifth meta- 
carpal bones, connecting them together. It is blended with the volar (glenoid) 



332 



SYNDESMOLOGY 



ligamehts of the metacarpophalangeal articulations. Its volar surface is concave 
where the Flexor tendons pass over it ; behind it the tendons of the Interossei pass 
to their insertions. 

X. Metacarpophalangeal Articulations (Articulationes Metacarpophalangese ; 
Metacarpophalangeal Joints) (Figs. 337, 338). 

These articulations are of the condyloid kind, formed by the reception of the 
rounded heads of the metacarpal bones into shallow cavities on the proximal ends 
of the first phalanges, with the exception of that of the thumb, which presents 
more of the characters of a ginglymoid joint. Each joint has a volar and two 
collateral ligaments. 



Metacarpal hone ■ 



Transverse 
nietacarpal — ^^5 
ligament 

Groove for 
Flexor tendons 



1st phalanx 



Volar ligament 



Volar ligament 



i\ , 



,\VM 



Metacarpal 

bone \ 



3rd phalanx 




Collateral 
ligament 



Collateral 
ligament 



2nd phalanx 



Collateral 
ligament 



Fig. 337. — Metacarpophalangeal articulation and 
articulations of digit. Volar aspect. 



Fig. 



338. — Metacarpophalangeal articulation 
articulations of digit. Ulnar aspect. 



and 



The Volar Ligaments {glenoid ligaments of Criiveilhier; palmar or vaginal ligaments). 
-^The volar ligaments are thick, dense, fibrocartilaginous structures, placed upon 
the volar surfaces of the joints in the intervals between the collateral ligaments, to 
which they are connected ; they are loosely united to the metacarpal bones, but are 
very firmly attached to the bases of the first phalanges. Their volar surfaces are 
intimately blended with the transverse metacarpal ligament, and present grooves 
for the passage of the Flexor tendons, the sheaths surrounding which are connected 
to the sides of the grooves. Their deep surfaces form parts of the articular facets 
for the heads of the metacarpal bones, and are lined by synovial membranes. 

The Collateral Ligaments {ligamenta collateralia; lateral ligaments). — The col- 
lateral ligaments are strong, rounded cords, placed on the sides of the joints; 



COXAL ARTICULATION OR HIP- JOINT 333 

each is attached by one extremity to the posterior tubercle and adjacent depres- 
sion on the side of the head of the metacarpal bone, and by the other to the 
contiguous extremity of the phalanx. 

The dorsal surfaces of these joints are covered by the expansions of the Extensor 
tendons, together with some loose areolar tissue which connects the deep surfaces 
of the tendons to the bones. 

Movements. — The movements which occur in these joints are flexion, extension, adduction, 
abduction, and circumduction; the movements of abduction and adduction are very Umited, 
and cannot be performed when the fingers are flexed. 

XI. Articulations of the Digits (Articulationes Digitorum Manus ; Interphalangeal 

Joints) (P'igs. ;:i;37, ;33cS). 

The interphalangeal articulations are hinge-joints; each has a volar and two 
collateral ligaments. The arrangement of these ligaments is similar to those in 
the metacarpophalangeal articulations. The Extensor tendons supply the place 
of posterior ligaments. 

Movements, — The only movements permitted in the interphalangeal joints are flexion and 
extension; these movements are more extensive between the first and second phalanges than 
between the second and third. The amoimt of flexion is very considerable, but extension is 
limited by the volar and collateral ligaments. 

Muscles Acting on the Joints of the Digits. — Flexion of the metacarpophalangeal joints of the 
fingers is effected by the Flexores digitorum subUmis and profundus, Lumbricales, and Interossei, 
assisted in the case of the little finger by the Flexor digiti quinti brevis. Extension is produced 
by the Extensor digitorum communis, Extensor indicis proprius, and Extensor digiti quinti pro- 
prius. 

Flexion of the interphalangeal joints of the fingers is accomphshed by the Flexor digitorum 
profundus acting on the proximal and distal joints and by the Flexor digitorum sublimis acting 
on the proximal joints. Extension is effected mainly by the Lumbricales and Interossei, the 
long Extensors having httle or no action upon these joints. 

Flexion of the metacarpophalangeal joint of the thumb is effected by the Flexores polTlcis 
longus and brevis; extension by the Extensores pollicis longus and brevis. Flexion of the inter- 
phalangeal joint is accomplished by the Flexor pollicis longus, and extension by the Extensor 
pollicis longus. 

ARTICULATIONS OF THE LOWER EXTREMITY. 

The articulations of the Lower Extremity comprise the following: 

I. Hip. V. Intertarsal. 

II. Knee. VI. Tarsometatarsal. 

III. Tibiofibular. VII. Intermetatarsal. 

IV. Ankle. VIII. Metatarsophalangeal. 

IX. Articulations of the Digits. 

I. Coxal Articulation or Hip-joint (Articulatio Coxae). 

This articulation is an enarthrodial or ball-and-socket joint, formed by the 
reception of the head of the femur into the cup-shaped cavity of the acetabulum. 
The articular cartilage on the head of the femur, thicker at the center than at the 
circumference, covers the entire surface with the exception of the fovea capitis 
femoris, to which the ligamentum teres is attached; that on the acetabulum forms 
an incomplete marginal ring, the lunate surface. Within the lunate surface there 
is a circular depression devoid of cartilage, occupied in the fresh state by a mass 
of fat, covered by synovial membrane. The ligaments of the joint are: 

The Articular Capsule. The Pubocapsular. 

The Iliofemoral. The Ligamentum Teres Femoris. 

The Ischiocapsular. The Glenoidal Labrum. 

The Transverse Acetabular 



334 



SYNDESMOLOGY 



The Articular Capsule (capsula articularis; capsular ligament) (Figs. 339, 340). — 
The articular capsule is strong and dense. Above, it is attached to the margin 
of the acetabulum 5 to 6 mm. beyond the glenoidal labrum behind; but in front, 
it is attached to the outer margin of the labrum, and, opposite to the notch where 
the margin of the cavity is deficient, it is connected to the transverse ligament, 
and by a few fibers to the edge of the obturator foramen. It surrounds the neck 
of the femur, and is attached, in front, to the intertrochanteric line; above, to the 
base of the neck; behind, to the neck, about 1.25 cm. above the intertrochanteric 
crest; beloiv, to the lower part of the neck, close to the lesser trochanter. From 
its femoral attachment some of the fibers are reflected upward along the neck 
as longitudinal bands, termed retinacula. The capsule is much thicker at the upper 
and forepart of the joint, where the greatest amount of resistance is required; 



Ani. inf. iliac spine — 




Intertrochanteric 
line 



Pig. 339. — Right hip-joint from the front. (Spalteholz.) 



behind and below, it is thin and loose. It consists of two sets of fibers, circular 
and longitudinal. The circular fibers, zona orbicularis, are most abundant at the 
lower and back part of the capsule (Fig. 342), and form a sling or collar around the 
neck of the femur. Anteriorly they blend with the deep surface of the iliofemoral 
ligament, and gain an attachment to the anterior inferior iliac spine. The longi- 
tudinal fibers are greatest in amount at the upper and front part of the capsule, 
where they are reinforced by distinct bands, or accessory ligaments, of which the 
most important is the iliofemoral ligament. The other accessory bands are known 
as the pubocapsular and the ischiocapsular ligaments. The external surface of the 
capsule is rough, covered by numerous muscles, and separated in front from the 
Psoas major and Iliacus by a bursa, which not infrequently commimicates by a 
circular aperture with the cavity of the joint. 



COXAL ARTICULATION OR HIP-JOINT 335 

The mofemoral Ligament (/.:^amen^um iliofemorale; Y -ligament; ligament of 
Bigeloic) (Fig «9).-lhe iliofemoral ligament is a band of great s rength which 
hes m front of the jomt; it is mtimately connected with the capsule, and ser es 
to strengthen It m this situation. It is attached, above, to the lower part of the 
anterior inferior ilmc spine; 6./oz., it divides into two bands, one of which passes 
downward a^nd is fixed to the lower part of the intertrochanteric line; the other 
IS directed downward and lateralward and is attached to the upper part of the 
same line. Between the two bands is a thinner part of the capsule. In some 
cases there IS no division, and the ligament spreads out into a flat triangular band 
which IS attached o the whole length of the intertrochanteric line. This ligament 
IS frequently called the \ -shaped ligament of Bigelow; and its upper band is some- 
times named the iliotrochanteric ligament. 



Horizontal fibers 

Ischiofemoral ligament 




Fig 340 — The hip-joint from behind. (Quain.) 

The Pubocapsular Ligament {Ugamentuvi p^ibocapsulare; 'piihofevtoral ligament). — 
This ligament is attached, above, to the obturator crest and the superior ramus 
of the pubis; beloio, it blends with the capsule and with the deep surface of the 
vertical band of the iliofemoral ligament. 

The Ischiocapsular Ligament {ligamentum iscJiiocapsnlare; ischiocapsular band; 
ligament of Bertin). — The ischiocapsular ligament consists of a triangular band of 
strong fibers, which spring from the ischium below and behind the acetabulum, 
and blend with the circular fibers of the capsule (Fig. 340). 



330 



SYNDESMOLOGY 



The Ligamentum Teres Femoris (Fig. 341). — The ligamentum teres femoris is a 
triangular, somewhat flattened band implanted by its apex into the antero-superior 
part of the fovea capitis femoris ; its base is attached by two bands, one into either 
side of the acetabular notch, and between these bony attachments it blends with the 
transverse ligament. It is ensheathed by the synovial membrane, and varies greatly 
in strength in different subjects; occasionally only the synovial fold exists, and in 
rare cases even this is absent. The ligament is made tense M'hen the thigh is 
semiflexed and the limb then adducted or rotated outward; it is, on the other 
hand, relaxed when the limb is abducted. It has, however, but little influence as a 
ligament. 



Spine of 
ischimu 




Ant. inf. 
"^ iliac spine 



■Fovea capitis 



Iliofemoral ligament 



Lesser trochanter 



Fig. 341. — Left hipHJoint, opened by removiug the llour of the acetabulum from within the pelvis. 



The Glenoidal Labnim {labrum glenoidalc; cotyloid ligament). — The glenoidal 
labrum is a fibrocartilaginous rim attached to the margin of the acetabulum, the 
cavity of which it deepens ; at the same time it protects the edge of the bone, and 
fills up the inequalities of its surface. It bridges over the notch as the transverse 
ligament, and thus forms a complete circle, which closely surrounds the head of the 
femur and assists in holding it in its place. It is triangular on section, its base being 
attached to the margin of the acetabulum, while its opposite edge is free and 
sharp. Its two surfaces are invested by synovial membrane, the external one 
being in contact with the capsule, the internal one being inclined inward so as 
to narrow the acetabulum, and embrace the cartilaginous surface of the head of 
the femur. It is much thicker above and behind than below and in front, and 
consists of compact fibers. 

The Transverse Acetabular Ligament (ligamentum transversum acetabuli; transverse 
ligament). — This ligament is in reality a portion of the glenoidal labrum, though 
differing from it in having no cartilage cells among its fibers. It consists of strong, 



COXAL ARTICULATION OR HIP-JOINT 



337 



%::!mt'\: ' 




Fig. 342. — Hip-joint, front view. The capsular ligament has been largely removed. 



Spine of 
ischium 



Capsule 

Greater trochanter 




Fig. 343. — Capsule of hip-joint (distended). Posterior aspect. 



22 



338 



SYNDESMOLOGY 



flattened fibers, which cross the acetabular notch, and convert it into a foramen 
through which the nutrient vessels enter the joint. 

Synovial Membrane (Fig. 343). — The synovial membrane is very extensive. Commencing 
at the margin of the cartilaginous surface of the head of the femur, it covers the portion of the 
neck which is contained within the joint; from the neck it is reflected on the internal surface of 
the capsule, covers both surfaces of the glenoidal labrum and the mass of fat contained in the 
depression at the bottom of the acetabulum, and ensheathes the ligamentum teres as far as the 
head of the femur. The joint ca\-ity sometimes communicates through a hole in the capsule 
between the vertical band of the ihofemoral ligament and the pubocapsular ligament with a bursa 
situated on the deep surfaces of the Psoas major and Ihacus. 

The muscles in relation with the joint are, in front, the Psoas major and Ihacus, separated 
from the capsule by a bursa; above, the reflected head of the Rectus femoris and Gluta^us minimus, 
the latter being closely adherent to the capsule; medially, the Obturator extemus and Pectineus; 
behind, the Piriformis, Gemellus superior, Obturator internus, Gemellus inferior, Obturator 
extemus, and Quadratus femoris (Fig. 344). 

Femoral artery 
Femoral nerve j Femoral vein, 
Iliofevwral ligament I | i Ligamentum teres 

Rectus femoris ( ( / Obturator n-erve 




Piriformis I Sciatic nerve 

Obturator internus 
Fig. 344. — Structures surrounding right hip-joint. 



The arteries supplying the joint are derived from the obturator, medial femoral circumflex, 
and superior and inferior gluteals. 

The nerves are articular branches from the sacral plexus, sciatic, obturator, accessory obtm'ator, 
and a filament from the branch of the femoral supplying the Rectus femoris. 

Movements. — The movements of the hip are very extensive, and consist of flexion, extension, 
adduction, abduction, circumduction, and rotation. 

The length of the neck of the femur and its inclinations to the body of the bone have the 
effect of converting the angular movements of flexion, extension, adduction, and abduction par- 
tially into rotatory movements in the joint. Thtis when the thigh is flexed or extended, the 
head of the femtir, on account of the medial inclination of the neck, rotates within the acetabulum 
with only a shght amount of gliding to and fro. The forward slope of the neck similarly affects 
the movements of adduction and abduction. Conversely rotation of the thigh which is permitted 
by the upward inclination of the neck, is not a simple rotation of the head of the femvir in the 
acetabulum, but is accompanied by a certain amount of gliding. 



THE KNEE-JOINT 339 

The hip-joint presents a very striking contrast to the shoulder-joint in the much more com- 
plete mechanical arrangements for its security and for the limitation of its movements. In the 
shoulder, as has been seen, the head of the humerus is not adapted at all in size to the glerioid 
cavity, and is hardly restrained in any of its ordinary movements by the capsule. In the hip- 
joint, on the contrary, the head of the femur is closely fitted to the acetabulum for an area extend- 
ing over nearly half a sphere, and at the margin of the bony cup it is still more closely embraced 
by the glenoidal labrum, so that the head of the femur is held in its place by that ligament even 
when the fibers of the capsule have been quite divided. The iliofemoral ligament is the strongest 
of all the ligaments in the body, and is put on the stretch by any attempt to extend the femur 
beyond a straight line with the trunk. That is to say, this ligament is the chief agent in main- 
taining the erect position without muscular fatigue; for a vertical hne passing through the center 
of gravity of the trunk falls behind the centers of rotation in the hip-joints, and therefore the 
pelvis tends to fall backward, but is prevented by the tension of the ihofemoral ligaments. The 
security of the joint may be provided for also by the two bones being directly united through the 
ligamentum teres; but it is doubtful whether this ligament has much influence upon the mechanism 
of the joint. When the knee is flexed, flexion of the hip-joint is arrested by the soft parts of the 
thigh and abdomen being brought into contact, and when the knee is extended, by the action of 
the hamstring muscles; extension is checked by the tension of the iliofemoral hgament; adduc- 
tion by the thighs coming into contact; adduction with flexion by the lateral band of the ilio- 
femoral hgament and the lateral part of the capsule; abduction by the medial band of the 
iliofemoral ligament and the pubocapsular Hgament; rotation outward by the lateral band of the 
ihofemoral ligament; and rotation inward by the ischiocapsular hgament and the hinder part of 
the capsule. The muscles which /ex the femur on the pelvis are the Psoas major, Ihacus, Rectus 
femoris, Sartorius, Pectineus, Adductores longus and brevis, and the anterior fibers of the Gluta?i 
medius and minimus. Extension is mainly performed by the Glutaeus maximus, assisted by the 
hamstring muscles and the ischial head of the Adductor magnus. The thigh is adduded by the 
Adductores magnus, longus, and brevis, the Pectineus, the Gracihs, and lower part of the Glutaeus 
maximus, and abducted by the Gluta>i medius and minimus, and the upper part of the Glutceus 
maximus. The muscles which rotate the thigh inward are the Gluta>us minimus and the anterior 
fibers of the Glutaeus medius, the Tensor fasciae latse and the lUacus and Psoas major; while 
those which rotate it outward are the posterior fibers of the Gluteus medius, the Piriformis, 
Obturatores externus and intemus, Gemelli superior and inferior, Quadratus femoris, Glutajus 
maximus, the Adductores longus, brevis, and magnus, the Pectineus, and the Sartorius. 



n. The Knee-joint (Articulatio Genu). 

The knee-joint was formerly described as a ginglymus or hinge-joint, but is 
really of a much more complicated character. It must be regarded as consisting 
of three articulations in one: two condyloid joints, one between each condyle 
of the femur and the corresponding meniscus and condyle of the tibia; and a third 
between the patella and the femur, partly arthrodial, but not completely so, 
since the articular surfaces are not mutually adapted to each other, so that the 
movement is not a simple gliding one. This view of the construction of the knee- 
joint receives confirmation from the study of the articulation in some of the lower 
mammals, where, corresponding to these three subdivisions, three synovial cavities 
are sometimes found, either entirely distinct or only connected together by small 
communications. This view is further rendered probable by the existence in the 
middle of the joint of the two cruciate ligaments, which must be regarded as 
the collateral ligaments of the medial and lateral joints. The existence of the 
patellar fold of synovial membrane would further indicate a tendency to separa- 
tion of the synovial cavity into two minor sacs, one corresponding to the lateral 
and the other to the medial joint. 

The bones are connected together by the following ligaments: 

The Articular Capsule. The Anterior Cruciate. 

The Ligamentum Patellae. The Posterior Cruciate. 

The Oblique Popliteal. The Medial and Lateral Menisci. 

The Tibial Collateral. The Transverse. 

The Fibular Collateral. The Coronary. 



340 



SYNDESMOLOGY 



The Articular Capsule {capmla articularis; capsular UgamenT) (Fig. 345). — The 
articular capsule consists of a thin, but strong, fibrous membrane ^vhich is strength- 
ened in almost its entire extent by bands inseparably connected with it. Above 
and in front, beneath the tendon of the Quadriceps femoris, it is represented only 
by the synovial membrane. Its chief strengthening bands are derived from the 
fascia lata and from the tendons surrounding the joint. In front, expansions 
from the Vasti and from the fascia lata and its iliotibial band fill in the intervals 
between the anterior and collateral ligaments, constituting the medial and lateral 
patellar retinacula. Behind the capsule consists of vertical fibers which a'-ise 
from the condyles and from the sides of the intercondyloid fossa of the femur; 

the posterior part of the capsule is therefore 
situated on the sides of and in front of the 
cruciate ligaments, which are thus excluded from 
the joint cavity. Behind the cruciate ligaments 
is the oblique popliteal ligament which is aug- 
mented by fibers derived from the tendon of the 
Semimembranosus. Laterally, a prolongation 
from the iliotibial band fills in the interval be- 
tween the oblique popliteal and the fibular collat- 
eral ligaments, and partly covers the latter. 
Medially, expansions from the Sartorius and 
Semimembranosus pass upward to the tibial 
collateral ligament and strengthen the capsule. 
The Ligamentimi Patellae {anterior ligament) 
(Fig. 345) . — The ligamentum patelli^ is the cen- 
tral portion of the common tendon of the Quad- 
riceps femoris, which is continued from the 
patella to the tuberosity of the tibia. It is a 
strong, flat, ligamentous band, about 8 cm. in 
length, attached, above, to the apex and adjoin- 
ing margins of the patella and the rough depres- 
sion on its posterior surface; below, to the 
tuberosity of the tibia; its superficial fibers are 
continuous over the front of the patella with 
those of the tendon of the Quadriceps femoris. 
The medial and lateral portions of the tendon 
of the Quadriceps pass down on either side of 
the patella, to be inserted into the upper extremity 
of the tibia on either side of the tuberosity ; these 
portions merge into the capsule, as stated above, 
forming the medial and lateral patellar retinacula. The posterior surface of the 
ligamentum patella is separated from the synovial membrane of the joint by a 
large infrapatellar pad of fat, and from the tibia by a bursa. 

The Oblique Popliteal Ligament {ligamentum popliteum obliquum; posterior liga- 
merit) (Fig. 346). — This ligament is a broad, flat, fibrous band, formed of fasciculi 
separated from one another by apertures for the passage of vessels and nerves. 
It is attached above to the upper margin of the intercondyloid fossa and posterior 
surface of the femur close to the articular margins of the condyles, and below to 
the posterior margin of the head of the tibia. Superficial to the main part of the 
ligament is a strong fasciculus, derived from the tendon of the Semimembranosus 
and passing from the back part of the medial condyle of the tibia obliquely upward 
and lateralward to the back part of the lateral condyle of the femur. The oblique 
popliteal ligament forms part of the floor of the popliteal fossa, and the popliteal 
artery rests upon it. 




Fig. 345. — Right knee-joint, 
view. 



Anterior 



THE KNEE-JOINT 



341 



The Tibial Collateral Ligament (ligamentum coUaierale tibiale; internal lateral liga- 
ment) (Fig. 345). — The tibial collateral is a broad, flat, membranous band, situated 
nearer to the back than to the front of the joint. It is attached, above, to the medial 
condyle of the femur immediately below the adductor tubercle; hclow, to the medial 
condyle and medial surface of the body of the tibia. The fibers of the posterior 
part of the ligament are short and incline backward as they descend; they are 
inserted into the tibia above the groove for the Semimembranosus. The anterior 
part of the ligament is a flattened band, about 10 cm. long, which inclines forward 
as it descends. It is inserted into the medial surface of the body of the tibia about 
2.5 cm. below the level of the condyle. It is crossed, at its lower part, by the 
tendons of the Sartorius, Gracilis, and Semitendinosus, a bursa being interposed. 
Its deep surface covers the inferior medial genicular vessels and nerve and the 
anterior portion of the tendon of the Semimembranosus, with which it is connected 
by a few fibers; it is intimately adherent to the medial meniscus. 





Fig. 346. — Right knee-joint. Posterior view. 



Fig. 347- — Right knee-joint, from the front, 
showing interior ligaments. 



The Fibular Collateral Ligament ijlgamentum coUaierale fihidare; external lateral or 
long external lateral ligament) (Fig. 348) .-The fibular collateral is a strong rounded 
fibrous cord, attached, above, to the back part of the lateral condyle of the emi^ 
immediatelv above the groove for the tendon of the Popliteus; Mow, to the latera 
side of the head of the fibula, in front of the styloid process. The greater part of 
its lateral surface is covered by the tendon of the Biceps Temoris; th^ tendon, 
however, divides at its insertion into two parts, which are separated by the liga- 
ment. Deep to the ligament are the tendon of the Popliteus, ^"d the infer o 
lateral genicular vessels and nerve. The ligament has no attachment to the lateral 
meniscus. 



342 



SYNDESMOLOGY 



An inconstant bundle of fibers, the short fibular collateral ligament, is placed behind and 
parallel with the preceding, attached, above, to the lower and back part of the lateral condyle 
of the femur; below, to the summit of the stjdoid process of the fibula. Passing deep to it are 
the tendon of the Popliteus, and the inferior lateral genicular vessels and nerve. 

The Cruciate Ligaments {ligamenta cruciaia genu; crucial ligaments). — The cru- 
ciate ligaments are of considerable strength, situated in the middle of the joint, 
nearer to its posterior than to its anterior surface. They are called cruciate because 
they cross each other somewhat like the lines of the letter X; and have received 
the names anterior and posterior, from the position of their attachments to the 
tibia. 

■ The Anterior Cruciate Ligament {ligamentum cruciatum anterius; external crucial 
ligament) (Fig. 347) is attached to the depression in front of the intercondyloid 
eminence of the tibia, being blended with the anterior extremity of the lateral 
meniscus; it passes upward, backward, and lateralward, and is fixed into the medial 
and back part of the lateral condyle of the femur. 



Ant. cniciateligament 
Tendon of Po'pliteus 

Lateral meniscus 

Fibular collateral 
ligament 




Ligament of 
Wrisberg 

Medial me7iiscu3 

Tibial collateral 
ligament 



Fig. 348. — l^eft knee-joint from behind, showing interior ligaments. 



The Posterior Cruciate Ligament {ligamentum cruciatum jMsterius; internal crucial 
ligament) (Fig. 348) is stronger, but shorter and less oblique in its direction, than 
the anterior. It is attached to the posterior intercondyloid fossa of the tibia, and 
to the posterior extremity of the lateral meniscus; and passes upward, forward, 
and medialward, to be fixed into the lateral and front part of the medial condyle 
of the femur. 

The Menisci (semilunar fihrocartilages) (Fig. 349). — The menisci are two crescentic 
lamellse, which serve to deepen the surfaces of the head of the tibia for articulation 
with the condyles of the femur. The peripheral border of each meniscus is thick, 
convex, and attached to the inside of the capsule of the joint ; the opposite border 



THE KNEE-JOINT 



343 



is thin, concave, and free. The upper surfaces of the menisci are concave, and 
in contact with the condyles of the femur; their lower surfaces are flat, and rest 
upon the head of the tibia; both surfaces are smooth, and in\ested by synovial 
membrane. Each meniscus covers approximately the peripheral two-thirds of 
the corresponding articular surface of the tibia. 

The medial meniscus {meniscus medialis; internal semilunar fihrocartilage) is 
nearly semicircular in form, a little elongated from before backward, and broader 
behind than in front; its anterior end, thin and pointed, is attached to the anterior 
intercondyloid_ fossa of the tibia, in front of the anterior cruciate ligament; its 
posterior end is fixed to the posterior intercondyloid fossa of the tibia, between 
the attachments of the lateral meniscus and the posterior cruciate ligament. 



Anterior cruciate ligament 



Transverse ligament 




Ligament of Wrisberg 
Posterior cruciate ligament 

F^G. 349. — Head of right tibia seen from above, showing menisci and attachments of ligaments. 



The lateral meniscus {meniscus lateralis; external semilunar fihrocartilage) is nearly 
circular and covers a larger portion of the articular surface than the medial one. 
It is grooved laterally for the tendon of the Popliteus, Avhich separates it from the 
fibular collateral ligament. Its anterior end is attached in front of the intercon- 
dyloid eminence of the tibia, lateral to, and behind, the anterior cruciate ligament, 
with which it blends; the posterior end is attached behind the intercondyloid 
eminence of the tibia and in front of the posterior end of the medial meniscus. 
The anterior attachment of the lateral meniscus is twisted on itself so that its 
free margin looks backward and upward, its anterior end resting on a sloping 
shelf of bone on the front of the lateral process of the intercondyloid eminence. 
Close to its posterior attachment it sends off a strong fasciculus, the ligament of 
Wrisberg (Figs. 348, 349), which passes upward and medialward, to be inserted 
into the medial condyle of the femur, immediately behind the attachment of the 
posterior cruciate ligament. Occasionally a small fasciculus passes forward to 
be inserted into the lateral part of the anterior cruciate ligament. The lateral 
meniscus gives off from its anterior convex margin a fasciculus which forms the 
transverse ligament. 

The Transverse Ligament {ligamentiim transversum genu). — The transverse liga- 
ment connects the anterior convex margin of the lateral meniscus to the anterior 
end of the medial meniscus; its thickness varies considerably in different subjects, 
and it is sometimes absent. 

The coronary ligaments are merely portions of the capsule, which connect the 
periphery of each meniscus with the margin of the head of the tibia. 



344 



SYNDESMOLOGY 



Synovial Membrane. — The synovial membrane of the knee-joint is the largest and most exten- 
sive in the bod}\ Commencing at the upper border of the patella, it forms a large cul-de-sac 
beneath the Quadriceps femoris (Figs. 350, 351) on the lower part of the front of the femur, 
and frequently communicates with a bursa interposed between the tendon and the front of the 
femur. The pouch of synovial membrane between the Quadriceps and front of the femur is 
supported, during the movements of the knee, by a small muscle, the Articularis genu, which 
is inserted into it. On either side of the pateUa, the synovial membrane extends beneath the 
aponeuroses of the Vasti, and more especially beneath that of the Vastus medialis. Below the 
patella it is separated from the ligamentum pateUse by a considerable quantity of fat, known as 



Oblique popliteal 
ligament 



Medial meniscus 




Adipose tissue 



Bursa under Quadriceps 
ffl.maris 



Medial meniscus 



Ligamentum patellae 

Bursa between tibia and 
ligamentum patelloB 



Fio. 350. — Sagittal section of right knee-joint. 



the infrapatellar pad. From the medial and lateral borders of the articular surface of the patella, 
reduplications of the synovial membrane project into the interior of the joint. These form two 
fringe-like folds termed the alar folds ; below, these folds converge and are continued as a single 
band, the patellar fold (ligamentum mucosum), to the front of the intercondyloid fossa of the femur. 
On either side of the joint, the synovial membrane passes downward from the femm-, lining the 
capsule to its point of attachment to the menisci; it may then be traced over the upper surfaces 
of these to their free borders, and thence along their under surfaces to the tibia (Figs. 351, 352). 
At the back part of the lateral meniscus it forms a cul-de-sac between the groove on its surface 
and the tendon of the PopUteus; it is reflected across the front of the cruciate ligaments, which 
are therefore situated outside the synovial cavity. 



THE KNEE-JOINT 



345 



Bursse.— The bursae near the knee-joint are the following: In front there ViVo. four bursa;- a 
large one is interposed between the patella and the skin, a small one between the upper part of 
the tibia and the hgartientum patella-, a third between the lower part of the tuberosity of the 
tibia and the skin, and a fourth between the anterior surface of the lower part of the femur and 
the deep surface of the Quadriceps femoris, usually communicating with the knee-joint. Laterally 
there are four bursa;: (1) one (which sometimes communicates with the joint) between the 
lateral head of the Gastrocnemius and the capsule; (2) one between the fibular collateral ligament 
and the tendon of the Biceps; (3) one between the fibular collateral ligament and the tendon of 
the Pophteus (tins is sometimes only an expansion from the next bursa) ; (4) one between the 
tendon of the Popliteus and the lateral condyle of the femur, usually an extension from the 
synovial membrane of the joint. Medially, there are five bursa;: (1) one between the medial 
head of the Gastrocnemius and the capsule; this sends a prolongation between the tendon of the 



Quadriceps 
Jemoria 



Fibular collateral 

ligament 

Tendon of Popliteus 

Lateral meniscus 




,„ — Ligamentum 

'M patella- 



FiQ. 351. — Capsule of right knee-joint (distended). Lateral aspect. 



medial head of the Gastrocnemius and the tendon of the Semimembranosus and often communi- 
cates with the joint; (2) one superficial to the tibial collateral ligament, between it and the tendons 
of the Sartorius, Gracilis, and Semitendinosus; (3) one deep to the tibial collateral Ugament, 
between it and the tendon of the Semimembranosus (this is sometimes only an expansion 
from the next bursa) ; (4) one between the tendon of the Semimembranosus and the head of 
the tibia; (5) occasionally there is a bursa between the tendons of the Semimembranosus and 
Semitendinosus. 

Structures Around the Joint. — In front, and at the sides, is the Quadriceps femoris; laterally 
the tendons of the Biceps femoris and Popliteus and the common peroneal nerve; medially, 
the Sartorius, Gracilis, Semitendinosus, and Semimembranosus; behind, the popUteal vessels 
and the tibial nerve, Popliteus, Plantaris, and medial and lateral heads of the Gastrocnemius, 
some lymph glands, and fat. 

The arteries supplying the joint are the highest genicular (anastomotica magna), a branch 



346 



SYNDESMOLOGY 



of the femoral, the genicular branches of the popliteal, the recurrent branches of the anterior 
tibial, and the descending branch from the lateral femoral circumflex of the profunda femoris. 

The nerves are derived from the obturator, femoral, tibial, and common peroneal. 

Movements. — The movements which take place at the knee-joint are flexion and extension, 
and, in certain positions of the joint, internal and external rotation. The movements of flexion 
and extension at this joint differ from those in a typical hinge-joint, such as the elbow, in that 
(a) the axis around which motion take^ place is not a fixed one, but shifts forward during extension 
and backward during flexion; (b) the commencement of flexion and the end of extension are 
accompanied by rotatory movements associated with the fixation of the limb in a position of 
great stability. The movement from full flexion to full extension may therefore be described 
in three phases: 

1, In the fully flexed condition the posterior parts of the femoral condyles rest on the corre- 
sponding portions of the meniscotibial surfaces, and in this position a sUght amount of simple 
rolling movement is allowed. 



Posterior cruciate 
ligament 

Medial meniscus 



Tibial collateral 
ligament 




Anterior cruciate 
ligament 

Lateral meniscus 

ibular collateral 
ligament 



Fia. 352. — Capsule of right knee-joint (distended). Posterior aspect. 



2. During the passage of the limb from the flexed to the extended position a gliding movement 
is superposed on the rolling, so that the axis, which at the commencement is represented by a 
line through the inner and outer condyles of the femur, gradually shifts forward. In this part 
of the movement, the posterior two-thirds of the tibial articular sm-faces of the two femoral 
condyles are involved, and as these have similar curvatures and are parallel to one another, they 
move forward equally. 

3. The lateral condyle of the femur is brought almost to rest by the tightening of the anterior 
cruciate ligament; it moves, however, slightly forward and medialward, pushing before it the 
anterior part of the lateral meniscus. The tibial surface on the medial condyle is prolonged 
farther forward than that on the lateral, and this prolongation is directed lateralward. When, 
therefore, the movement forward of the condyles is checked by the anterior cruciate hgament, 
continued muscular action causes the medial condyle, dragging with it the meniscus, to travel 
backward and medialward, thus producing an internal rotation of the thigh on the leg. When 
the position of full extension is reached the lateral part of the groove on the lateral condyle is 
pressed against the anterior part of the corresponding meniscus, while the medial part of the 




ARTICULATIONS BETWEEN THE TIBIA AND FIBULA 347 

groove rests on the articular margin in front of the lateral process of the tibial intercondyloid 
eminence. Into the groove on the medial condyle is fitted the anterior part of the medial meniscus, 
while the anterior cruciate hgament and the articular margin in front of the medial process of 
the tibial intercondyloid eminence are received into the forepart of the intercondyloid fossa of 
the femur. This third phase by which all these parts are brought into accurate apposition is 
known as the "screwing home," or locking movement of the joint. 

The complete movement of flexion is the converse of that described above, and is therefore 
preceded by an external rotation of the femur which unlocks the extended joint. 

The axes around which the movements of flexion and extension take place are not precisely 
at right angles to either bone; in flexion, the femur and tibia are in the same plane, but in exten- 
sion the one bone forms an angle, opening lateralward with the other. 

In addition to the rotatory movements associated with the completion of extension and the 
initiation of flexion, rotation inward or outward can be effected when the joint is partially flexed; 
these movements take place mainly between the tibia and the menisci, and are freest when the 
leg is bent at right angles with the thigh. 

Movements of Patella. — The articular surface of the patella is indistinctly divided into seven 
facets — upper, middle, and lower horizontal pairs, and a medial perpendicular facet (Fig. 353). 
When the knee is forcibly flexed, the medial perpendicular 
facet is in contact with the semilunar surface on the lateral 
part of the medial condyle; this semilunar surface is a pro- 
longation backward of the medial part of the patellar surface. 
As the leg is carried from the flexed to the extended position, 
first the highest pair, then the middle pair, and lastly the 
lowest pair of horizontal facets is successively brought into 
contact with the patellar surface of the femur. In the ex- 
tended position, when the Quadriceps femoris is relaxed, the 
patella lies loosely on the front of the lower end of the femur. 

During flexion, the ligamentum patellae is put upon 
the stretch, and in extreme flexion the posterior cruciate 

hgament, the obUque popliteal, and collateral Ugaments, ^ „ . , , , 

T , r Ui i i i-u J. ■ • X 1 • i Fig. 353— Posterior surface of the 

and, to a slight extent, the anterior cruciate hgament, right patella, showing diagrammaticaUy 

are relaxed. Flexion is checked during hfe by the contact ^}}% areas of contact with the femur in 

f ,, , -,, ,, ,!.• 1 TTT. .1 1 • ■ i • r 11 different position? of the knee, 

of the leg with the thigh. When the knee-joint is fuUy 

extended the obhque pophteal and collateral ligaments, 

the anterior cruciate ligament, and the posterior cruciate ligament, are rendered tense; 
in the act of extending the knee, the ligamentum patella; is tightened by the Quadriceps 
femoris, but in full extension with the heel supported it is relaxed. Rotation inward is checked 
by the anterior cruciate ligament; rotation outward tends to uncross and relax the cruciate hga- 
ments, but is checked by the tibial collateral hgament. The main function of the cruciate liga- 
ment is to act as a direct bond between the tibia and femur and to prevent the former bone from 
being carried too far backward or forward. They also assist the collateral hgaments in resisting 
any bending of the joint to either side. The menisci are intended, as it seems, to adapt the surfaces 
of the tibia to the shape of the femoral condj'les to a certain extent, so as to fill up the intervals 
which would otherwise be left in the varying positions of the joint, and to obviate the jars which 
would be so frequently transmitted up the hmb in jumping or by falls on the feet; also to permit 
of the two varieties of motion, flexion and extension, and rotation, as explained above. The 
patella is a great defence to the front of the knee-joint, and distributes upon a large and tolerably 
even surface, during kneeling, the pressure which would otherwise fall upon the prominent ridges 
of the condyles; it also affords leverage to the Quadriceps femoris. 

When standing erect in the attitude of "attention," the weight of the body falls in front of 
a line carried across the centers of the knee-joints, and therefore tends to produce overextension 
of the articulations; this, however, is prevented by the tension of the anterior cruciate, oblique 
pophteal, and collateral ligaments. 

Extension of the leg on the thigh is performed by the Quadriceps femoris; flexion by the Biceps 
femoris, Semitendinosus, and Semimembranosus, assisted by the GraciUs, Sartorius, Gastroc- 
nemius, Pophteus, and Plantaris. Rotation outward is effected by the Biceps femoris, and rota- 
tion inward by the Popliteus, Semitendinosus, and, to a shght extent, the Semimembranosus, the 
Sartorius, and the GraciHs. The Pophteus comes into action especially at the commencement 
of the movement of flexion of the knee; by its contraction the leg is rotated inward, or, if the 
tibia be fixed, the thigh is rotated outward, and the knee-joint is unlocked. 

in. Articulations between the Tibia and Fibula. 

The articulations between the tibia and fibula are effected by ligaments which 
connect the extremities and bodies of the bones. The ligaments may consequently 



34S ' SYNDESMOLOGY 

be subdivided into three sets: (1) those of the Tibiofibular articulation; (2) the 
interosseous membrane; (3) those of the Tibiofibular syndesmosis. 

Tibiofibular Articulation (articulatio Ubiofibidaris; superior tibiofibular articula- 
tion). — This articulation is an arthrodial joint between the lateral condyle of the 
tibia and the head of the fibula. The contiguous surfaces of the bones present 
flat, oval facets covered with cartilage and connected together by an articular 
capsule and by anterior and posterior ligaments. 

The Articular Capsule (capsula articularis; capsular ligament). — The articular 
capsule surrounds the articulation, being attached around the margins of the 
articular facets on the tibia and fibula; it is much thicker in front than 
behind. 

The Anterior Ligament {anterior superior ligament). — The anterior ligament of 
the head of the fibula (Fig. 347) consists of two or three broad and flat bands, 
which pass obliquely upward from the front of the head of the fibula to the front 
of the lateral condyle of the tibia. 

The Posterior Ligament {posterior superior ligament). — The posterior ligament of 
the head of the fibula (Fig. 348) is a single thick and broad band, which passes 
obliquely upward from the back of the head of the fibula to the back of the lateral 
condyle of the tibia. It is covered by the tendon of the Popliteus. 

Synovial Membrane. — A sjmovial membrane lines the capsule; it is continuous with that of 
the knee-joint in occasional cases when the two joints communicate. 

Interosseous Membrane {membrana interossea cruris; middle tibiofibular liga- 
ment). — An interosseous membrane extends between the interosseous crests of the 
tibia and fibula, and separates the muscles on the front from those on the back 
of the leg. It consists of a thin, aponeurotic lamina composed of oblique fibers, 
which for the most part run downward and lateralward; some few fibers, however, 
pass in the opposite direction. It is broader above than below. Its upper margin 
does not quite reach the tibiofibular joint, but presents a free concave border, 
above which is a large, oval aperture for the passage of the anterior tibial vessels 
to the front of the leg. In its lower part is an opening for the passage of the anterior 
peroneal vessels. It is continuous below with the interosseous ligament of the tibio- 
fibular syndesmosis, and presents numerous perforations for the passage of small 
vessels. It is in relation, in front, with the Tibialis anterior. Extensor digitorum 
longus. Extensor hallucis proprius, Perona^us tertius, and the anterior tibial 
vessels and deep peroneal nerve; behind, with the Tibialis posterior and Flexor 
hallucis longus. 

Tibiofibular Syndesmosis {syndesmosis tibiofibularis; inferior tibiofibular articu- 
lation). — This syndesmosis is formed by the rough, convex surface of the medial 
side of the lower end of the fibula, and a rough concave surface on the lateral side 
of the tibia. Below, to the extent of about 4 mm. these surfaces are smooth, and 
covered with cartilage, which is continuous with that of the ankle-joint. The 
ligaments are: anterior, posterior, inferior transverse, and interosseous. 

The Anterior Ligament {ligamentum malleoli lateralis anterius; anterior inferior 
ligament). — The anterior ligament of the lateral malleolus (Fig. 355) is a flat, 
triangular band of fibers, broader below than above, which extends obliquely 
downward and lateralward between the adjacent margins of the tibia and fibula, 
on the front aspect of the syndesmosis. It is in relation, in front, with the Peronseus 
tertius, the aponeurosis of the leg, and the integument ; behind, with the interosseous 
ligament; and lies in contact with the cartilage covering the talus. 

The Posterior Ligament {ligamentum malleoli lateralis posterius; posterior inferior 
ligament). — The posterior ligament of the lateral malleolus (Fig. 355), smaller 
than the preceding, is disposed in a similar manner on the posterior surface of 
the svndesmosis. 



TALOCRURAL ARTICULATION OR ANKLE-JOINT 



349 



The Inferior Transverse Ligament. — The inferior transverse ligament lies in front 
of the posterior ligament, and is a Strong, thick band, of yellowish fibers which 
passes transversely across the back of the joint, from the lateral malleolus to the 
posterior border of the articular surface of the tibia, almost as far as its malleolar 
process. This ligament projects below the margin of the bones, and forms part 
of the articulating surface for the talus. 

The Interosseous Ligament. — The interosseous ligament consists of numerous 
short, strong, fibrous bands, which pass between the contiguous rough surfaces of 
the tibia and fibula, and constitute the chief bond of union between the bones. 
It is continuous, above, with the interosseous membrane (Fig. 35G). 

Synovial Membrane. — The synovial membrane associated with the small arthrodial part of 
this joint is continuous with that of the ankle-joint. 

IV. Talocrural Articulation or Ankle-joint (Articulatio Talocruralis ; Tibiotarsal 

Articulation) . 

The ankle-joint is a ginglymus, or hinge-joint. The structures entering into its 
formation are the lower end of the tibia and its malleolus, the malleolus of the 




^' Post, talotibial ligament 



Medial talpcalcaneal lig. 

Post, talocalcaneal lig. 

1 



1 !. 

Articular capsule Medial cuneonavic. lig. 

Calcaneocuboid ligament 

Plantar calcaneonaoic. 
liaarnent 

Long plantar ligament 

Fig. 354. — tigaments of the medial aspect of the foot. (Quain.) 

fibula, and the transverse ligament, which together form a mortise for the recep- 
tion of the upper convex surface of the talus and its medial and lateral facets. 
The bones are connected by the following ligaments: 



The Articular Capsule. 
The Deltoid. 



The Anterior Talofibular. 
The Posterior Talofibular. 



The Calcaneofibular. 



350 



SYNDESMOLOGY 



The Articular Capsule (capsula articidaris; capsular ligament). — The articular cap- 
sule surrounds the joints, and is attached, above, to the borders of the articular 
surfaces of the tibia and malleoli; and below, to the talus around its upper articular 
surface. The anterior part of the capsule {anterior ligament) is a broad, thin, 
membranous layer, attached, above, to the anterior margin of the lower end of 
the tibia; below, to the talus, in front of its superior articular surface. It is in 
relation, in front, with the Extensor tendons of the toes, the tendons of the Tibialis 
anterior and Peronj^tus tertius, and the anterior tibial vessels and deep peroneal 
nerve. The posterior part of the capsule (posterior ligament) is very thin, and 
consists principally of transverse fibers. It is attached, above, to the margin of the 
articular surface of the tibia, blending with the transverse ligament; below, to the 
talus behind its -superior articular facet. Laterally, it is somewhat thickened, and 
is attached to the hollow on the medial surface of the lateral malleolus. 



Ant. lat. jnalleol. lig 



Post. lat. malleol. lig._ 



Dorsal talonavic. lia. 

XCalcaneonaiic. Tparl\^.. , ,. 

, I Calcaneocuboid part]^'^'^'"^^^ ^^^ 
j I I Dorsal cuboideonavic. lig. 

Dorsal navicular cuneif. lig. ■ 

/ Dorsal cuneocuboid lig. 
' \Dorsal intercuneif. lig. 

/^/ Dorsal tarsometat. lia 



Post, talofibular lig. _ 




J plantar Hi,, 
jinteros. talocalcan. lig. 
Ant. talofibular lig. 



Dorsal intermet. lig. 
Dorsal tarsomet. lig. 



Calcaneo fibular lig. 
Fig. 355. — The ligaments of the foot from the lateral aspect, (t^uain.) 

The Deltoid Ligament (ligameninm deltoideum; internal lateral ligament) 
(Fig. 331). — The deltoid ligament is a strong, flat, triangular band, attached, 
above, to the apex and anterior and posterior borders of the medial malleolus. 
It consists of two sets of fibers, superficial and deep. Of the superficial fibers the 
most anterior {tibionavicular) pass forward to be inserted into the tuberosity of 
the navicular bone, and immediately behind this they blend with the medial margin 
of the plantar calcaneonavicular ligament; the middle {calcaneotibial) descend 
almost perpendicidarly to be inserted into the whole length of the sustentaculum 
tali of the calcaneus; the posterior fibers {posterior talotibial) pass backward and 
lateralward to be attached to the inner side of the talus, and to the prominent 



TALOCRURAL ARTICULATION OR ANKLE-JOINT 



351 



tubercle on its posterior surface, medial to the groove for the tendon of the Flexor 
hallucis longus. The deep fibers {anterior talotibial) are attached, above, to the 
tip of the medial malleolus, and, beloiv, to the medial surface of the talus. The 
deltoid ligament is covered by the tendons of the Tibialis posterior and Flexor 
digitorum longus. 

The anterior and posterior talofibular and the calcaneofibular ligaments were 
formerly described as the three fasciculi of the external lateral ligament of the 
ankle-joint. 

The Anterior Talofibular Ligament {ligamentum talofibulare anterius) (Fig. 355). 
— The anterior talofibular ligament, the shortest of the three, passes from the 
anterior margin of the fibular malleolus, forward and medially, to the talus, in 
front of its lateral articular facet. 

The Posterior Talofibular Ligament {ligamentum talofibulare jjosterius) (Fig. 355). 
— The posterior talofibular ligament, the strongest and most deeply seated, runs 
almost horizontally from the depression at the medial and back part of the fibular 
malleolus to a prominent tubercle on the posterior surface of the talus immediately 
lateral to the groove for the tendon of the Flexor hallucis longus. 

The Calcaneofibular Ligament {ligamentum calcaneofibulare) (Fig. 355). — The 
calcaneofibular ligament, the longest of the three, is a narrow, rounded cord, run- 
ning from the apex of the fibular malleolus downward and slightly backward to a 
tubercle on the lateral surface of the calcaneus. It is covered by the tendons of 
the Peronffii longus and brevis. 




Anterior talofibular lifjament 

Posterior talofibular ligament 
Calcaneofibular ligamrnt 
Lateral talocalcaneal ligament 



Anterior 

talocalcaneal 

ligament 



Fig. 356. — Capsule of left talocrura articulation (distended). Lateral aspect. 



Synovial Membrane (Fig. 356). — The synovial membrane invests the deep surfaces of the 
ligaments, and sends a small process upward between the lower ends of the tibia and fibula. 

Relations.— The tendons, vessels, and nerves in connection with the joint are, in front, from the 
medial side, the Tibiahs anterior. Extensor hallucis proprius, anterior tibial vessels, deep peroneal 
nerve. Extensor digitorum longus, and Peronseus tertius; behind, from the medial side, the Tibialis 
posterior, Flexor digitorum longus, posterior tibial vessels, tibial nerve, Flexor haUucis longus; 
and, in the groove behind the fibular malleolus, the tendons of the Perona^i longus and brevis. 

The arteries supplying the joint are derived from the malleolar branches of the anterior tibial 
and the peroneal. 

The nerves are derived from the deep peroneal and tibial. 

Movements.— When the body is in the erect position, the foot is at right angles to the leg. 
The movements of the joint are those of dorsiflexion and extension; dorsiflexion consists in the 



352 SYNDESMOLOGY 

approximation of the dorsum of the foot to the front of the leg, while in extension the heel is 
drawn up and the toes pointed downward. The range of movement varies in different individuals 
from about 50° to 90°. The transverse axis about which movement takes place is slightly oblique. 
The malleoli tightly embrace the talus in all positions of the joint, so that any slight degree of 
side-to-side movement which may exist is simply due to stretching of the hgaments of the talo- 
fibular syndesmosis, and slight bending of the body of the fibula. The superior articular surface 
of the talus is broader in front than behind. In doisiflexion, herefore, greater space is required 
between the two malleoli. This is obtained by a slight outward rotatory movement of the lower 
end of the fibula and a stretching of the ligaments of the syndesmosis ; this lateral movement is 
facilitated by a slight ghding at the tibiofibular articulation, and possibly also by the bending of 
the body of the fibula. Of the ligaments, the deltoid is of very great power — so much so, that 
it usually resists a force which fractures the process of bone to which it is attached. Its middle 
portion, together with the calcaneofibular hgament, binds the bones of the leg firmly to the 
foot, and resists displacement in every direction. Its anterior and posterior fibers limit extension 
and flexion of the foot respectively, and the anterior fibers also limit abduction. The posterior 
talofibular ligament assists the calcaneofibular in resisting the displacement of the foot back- 
ward, and deepens the cavity for the reception of the talus. The anterior talofibular is a 
security against the displacement of the foot forward, and hmits extension of the joint. 

The movements of inversion and eversion of the foot, together with the minute changes in 
form by which it is applied to the ground or takes hold of an object in climbing, etc., are mainly 
effected in the tarsal joints; the joint which enjoys the greatest amount of motion being that be- 
tween the talus and calcaneus behind and the navicular and cuboid in front. This is often called 
the transverse tarsal joint, and it can, with the subordinate joints of the tarsus, replace the ankle- 
joint in a great measure when the latter has become ankylosed. 

Extension of the foot upon the tibia and fibula is produced by the Gastrocnemius, Soleus, 
Plantaris, Tibialis posterior, Perona-i longus and brevis. Flexor digitorum longus, and Flexor 
hallucis longus; dorsiflexion, by the Tibialis anterior, Peronaius tertius. Extensor digitorum longus, 
and Extensor hallucis proprius.^ 

V. Intertarsal Articulations (Articulationes Intertarseae ; Articulations 

of the Tarsus). 

Talocalcaneal Articulation {articulatio talocalcanea; articulation of the calcaneus 
and astragalus; calcaneo-astragaloid articulation). — The articulations between the 
calcaneus and talus are two in number^ — anterior and posterior. Of these, the 
anterior forms part of the talocalcaneonavicular joint, and will be described with 
that articulation. The posterior or talocalcaneal articulation is formed between 
the posterior calcaneal facet on the inferior surface of the talus, and the posterior 
facet on the superior surface of the calcaneus. It is an arthrodial joint, and the 
two bones are connected by an articular capsule and by anterior, posterior, lateral, 
medial, and interosseous talocalcaneal ligaments. 

The Articular Capsule (capsula articularis) .■ — The articular capsule envelops 
the joint, and consists for the most part of short fibers, which are split up into 
distinct slips; between these there is only a weak fibrous investment. 

The Anterior Talocalcaneal Ligament {lig amentum talocalcaneum anterius; anterior 
calcaneo-astragaloid ligament) (Figs. 356, 359). — The anterior talocalcaneal liga- 
ment extends from the front and lateral surface of the neck of the talus to 
the superior surface of the calcaneus. It forms the posterior boundary of the 
talocalcaneonavicular joint, and is sometimes described as the anterior interosseous 
ligament. 

The Posterior Talocalcaneal Ligament {ligamentum talocalcaneum posterius; 
posterior calcaneo-astragaloid ligament) (Fig. 354). — The posterior talocalcaneal 
ligament connects the lateral tubercle of the talus with the upper and medial part 
of the calcaneus; it is a short band, and its fibers radiate from their narrow attach- 
ment to the talus. 

The Lateral Talocalcaneal Ligament {ligamentum talocalcaneum laterale; external 
calcaneo-astragaloid ligament) (Figs. 356, 359). — The lateral talocalcaneal ligament 

1 The student must bear in mind that the Extensor digitorum longus and Extensor hallucis proprius are extensors 
of the toes, but flexors of the ankle; and that the Flexor digitorum longus and Flexor hallucis longus are flexors of the 
toes, but extensors of the ankle. 



INTERTARSAL ARTICULATIONS 



353 



is a short, strong fasciculus, passing from the lateral surface of the talus, imme- 
diately beneath its fibular facet to the lateral surface of the calcaneus. It is placed 
in front of, but on a deeper plane than, the calcaneofibular ligament, with the fibers 
of which it is parallel. 

The Medial Talocalcaneal Ligament (ligamentum talocalcaneum mediale; internal 
calcaneo-astragaloid ligament) .—The medial talocalcaneal ligament connects the 
medial tubercle of the back of the talus with the back of the sustentaculum tali. 
Its fibers blend with those of the plantar calcaneonavicular ligament (Fig. 354). 



Medial matleolus 

Deltoid ligament 

Tibialis posterior 



flexor digitorum longus' 

Flexor hallucis lotigus 

Med. plantar nerve and vessel 

Quadratus plantce 

Abductor hallucis 

Lat. plantar nerve and vessels 
Flexor digitorum brevis 




Interosseous ligament of tibio 
fibular syndesmosis 



Lateral malleolus 

Calcaneofibular ligament 
Interosseous talocalcaneal 
ligament 

Peronoeus brevis 



Peronceus longtis 
Abductor digiti quinti 



Fio. .357. — Coronal section through right talocrural and talocalcaneal joints. 

The Interosseous Talocalcaneal Ligament {ligamentum talocalcaneum inierosseum) 
(Figs. 357, 359). — The interosseous talocalcaneal ligament forms the chief bond 
of union between the bones. It is, in fact, a portion of the united capsules of the 
talocalcaneonavicular and the talocalcaneal joints, and consists of two partially 
united layers of fibers, one belonging to the former and the other to the latter joint. 
It is attached, above, to the groove between the articular facets of the under surface 
of the talus; below, to a corresponding depression on the upper surface of the cal- 
caneus. It is very thick and strong, being at least 2.5 cm. in breadth from side 
to side, and serves to bind the calcaneus and talus firmly together. 

Synovial Membrane (Fig. 360). — The synovial membrane lines the capsule of the joint, and 
is distinct from the other synovial membranes of the tarsus. 

Movements. — The movements permitted between the talus and calcaneus are limited to glid- 
ing of the one bone on the other backward and forward and from side to side. 

Talocalcaneonavicular Articulation (articulatio talocalcnneonancularis). — This 

articulation is an arthrodial joint: the rounded head of the talus being received 

into the concavity formed by the posterior surface of the navicular, the anterior 

articular surface of the calcaneus, and the upper surface of the plantar calcaneo- 

23 



354 SYXDESMOLOGY 

navicular ligament. There are two ligaments in this joint: the articular capsule 
and the dorsal talonavicular. 

The Articular Capsule {capsula ariicularis) . — The articular capsule is imperfectly 
developed except posteriorly, where it is considerably thickened and forms, with 
a part of the capsule of the talocalcaneal joint, the strong interosseous ligament 
which fills in the canal formed by the opposing grooves on the calcaneus and talus, 
as above mentioned. 

The Dorsal Talonavicular Ligament {ligamentum talonaviculare dorsale; superior 
astragalonavicular ligament) (Fig. 354). — This ligament is a broad, thin band, which 
connects the neck of the talus to the dorsal surface of the navicular bone; it is 
covered by the Extensor tendons. The plantar calcaneonavicular supplies the 
place of a plantar ligament for this joint. 

Synovial Membrane. — The synovial membrane lines all parts of the capsule of the joint. 

Movements. — Tliis articulation permits of a considerable range of gliding movements, and some 
rotation; its feeble construction allows occasionally of dislocation of the other bones of the tarsus 
from the talus. 

Calcaneocuboid Articulation {articulatio calcaneocuboidea; articulation of the 
calcaneus with the cuboid). — The ligaments connecting the calcaneus with the 
cuboid are five in number, viz., the articular capsule, the dorsal calcaneocuboid, 
part of the bifurcated, the long plantar, and the plantar calcaneocuboid. 

The Articular Capsule (capsula articularis). — The articular capsule is an imper- 
fectly developed investment, containing certain strengthened bands, which form 
the other ligaments of the joint. 

The Dorsal Calcaneocuboid Ligament (ligamentum calcaneocuhoideum dorsale; supe- 
rior calcaneocuboid ligament) (Fig. 355). — The dorsal calcaneocuboid ligament is 
a thin but broad fasciculus, which passes between the contiguous surfaces of the 
calcaneus and cuboid, on the dorsal surface of the joint. 

The Bifurcated Ligament (ligamentum bifurcatum; ijiternal calcaneocuboid; inter- 
osseous ligament) (Fig. 355, 359). — The bifurcated ligament is a strong band, 
attached behind to the deep hollow on the upper surface of the calcaneus and divid- 
ing in front in a Y-shaped manner into a calcaneocuboid and a calcaneonavicular 
part. The calcaneocuboid part is fixed to the medial side of the cuboid and forms 
one of the principal bonds between the first and second rows of the tarsal bones. 
The calcaneonavicular part is attached to the lateral side of the navicular. 

The Long Plantar Ligament (ligamentum plantare longum; long calcaneocuboid 
ligament; superficial long plantar ligament) (Fig. 358). — The long plantar ligament 
is the longest of all the ligaments of the tarsus: it is attached behind to the plantar 
surface of the calcaneus in front of the tuberosity, and in front to the tuberosity 
on the plantar surface of the cuboid bone, the more superficial fibers being con- 
tinued forward to the bases of the second, third, and fourth metatarsal bones. 
This ligament converts the groove on the plantar surface of the cuboid into a 
canal for the tendon of the Peronteus longus. 

The Plantar Calcaneocuboid Ligament (ligamentum calcaneocuboideum plantare; 
short calca)ieocuboid ligament; short plantar ligament) (Fig. 358).- — The plantar 
calcaneocuboid ligament lies nearer to the bones than the preceding, from which 
it is separated by a little areolar tissue. It is a short but wide band of great strength, 
and extends from the tubercle and the depression in front of it, on the forepart 
of the plantar surface of the calcaneus, to the plantar surface of the cuboid behind 
the peroneal groove. 

Synovial Membrane. — The synovial membrane lines the inner surface of the capsule and is 
distinct from that of the other tarsal articulations (Fig. 360). 

Movements. — The movements permitted between the calcaneus and cuboid are limited to 
slight gliding movements of the bones upon each other. 

The transverse tarsal joint is formed by the articulation of the calcane.is with the cuboid, and 



INTERTARSAL ARTICULATIONS 



355 



the articulation of the talus with the navicular. The movement which takes place in this joint 
is more extensive than that in the other tarsal joints, and consists of a sort of rotation by means 
of which the foot may be slightly flexed or extended, the sole being at the same time carried 
medially (.inverted) or laterally (everted). 

The Ligaments Connecting the Calcaneus and Navicular.— Though the calcaneus 
and na^•icula^ do not directly articulate, they are connected by two ligaments: 
the calcaneonavicular part of the bifurcated, and the plantar calcaneonavicular. 

The calcaneonavicular part of the bifurcated ligament is described on page 354. 



Plantar intcrmetatar. lig-.-M-X. 



Plantar calcaneocub. lig. — ; 



Tendon peroncms longus 
muscle 

Long plantar ligament 




Tendon peronceus 
^ longus muscle 



^-■'Plantar tarsometatar . lig. 



Tendon tibialis anticus 
muscle 



Plantar cuneonavic. lig. 

Plantar cuhoideonavic. 
ligament 

Plantar calcaneonavic. 
ligament 



Tendon tibialis posticus 
muscle 



Fig. 358.— Ligaments of the sole of the foot, with the tendons of tlie.Peronaeus longus, Tibialis posterior and Tibialis 

anterior muscles. (Quain.) 

The Plantar Calcaneonavicular Ligament {ligamentum calcaneonaviculare flantare; 
inferior or internal calcaneonavicular ligament; calcaneonavicular ligament) (Figs. 
354, 35<S).— The plantar calcaneonavicular ligament is a broad and thick band of 
fibers, which connects the anterior margin of the sustentaculum tali of the calca- 
neus to the plantar surface of the navicular. This ligament not only serves to 
connect the calcaneus and navicular, but supports the head of the talus, formmg 



35G 



SYNDESMOLOGY 



part of the articular cavity in which it is received. The dorsal surface of the 
ligament presents a fibrocartilaginous facet, lined by the synovial membrane, 
and upon this a portion of the head of the talus rests. Its plantar surface is 
supported by the tendon of the Tibialis posterior; its medial border is blended with 
the forepart of the deltoid ligament of the ankle-joint. 




Lateral 
ialocalcaneal 

ligament 

Anterior 
talocnlcaneal 

ligament 



Tibialis 
'posterior 



Interosseous 

ialocalcaneal 

ligament 



Fig. 359. — Talocalcaneal and talocalcaneonavicular articulations exposed from above by removing the talus. 

The plantar calcaneonavicular ligament, by supporting the head of the talus, is principally 
concerned in maintaining the arch of the foot. When it yields, the head of the talus is pressed 
downward, medialward, and forward by the weight of the body, and the foot becomes flattened, 
expanded, and turned lateralward, and exhibits the condition known as flat-foot. This ligament 
contains a considerable amount of elastic fibers, so as to give elasticity to the arch and spring 
to the foot; hence it is sometimes called the "spring" ligament. It is supported, on its plantar 
surface, by the tendon of the Tibialis posterior, which spreads out at its insertion into a number 
of fasciculi, to be attached to most of the tarsal and metatarsal bones. This prevents undue 
stretching of the ligament, and is a protection against the occurrence of flat-foot; hence muscular 
weakness is, in most cases, the primary cause of the deformity. 

Cuneonayicular Articulation (articidatio cuneonavicularis ; articulation of the 
navicular with the cuneiform hones). — The navicular is connected to the three 
cuneiform bones by dorsal and plantar ligaments. 

The Dorsal Ligaments {ligamenta navicularicuneijormia dorsalia). — The dorsal 
ligaments are three small bundles, one attached to each of the cuneiform bones. 
The bundle connecting the navicular with the first cuneiform is continuous around 
the medial side of the-articulation with the plantar ligament which unites these 
two bones (Figs. 354, 355) . 

The Plantar Ligaments (ligamenta navicularicuneiformia plantaria). — The plantar 
ligaments have a similar arrangement to the dorsal, and are strengthened by slips 
from the tendon of the Tibialis posterior (Fig. 358). 

Synovial Membrane. — The synovial membrane of these joints is part of the great tarsal synovial 
membrane (Fig. 360). 

Movements. — Mere gUding movements are permitted between the navicular and cuneiform 
bones. 

Cuboideonavicular Articulation. — The navicular bone is connected with the 
cuboid by dorsal, plantar, and interosseous ligaments. 



INTERTARSAL ARTICULATIONS 



357 



The Dorsal Ligament {ligameutum cuboideonaviculare dorsale) .—The dorsal ligament 
extends obliquely forward and lateralward from the navicular to the cuboid bone 
(Fig. 355). 

The Plantar Ligament {ligamentum cuboideonaoiculare plantare) .—The plantar 
ligament passes nearly transversely between these two bones (Fig. 358). 

The Interosseous Ligament.— The interosseous ligament consists of strong trans- 
verse fibers, and connects the rough non-articular portions of the adjacent surfaces 
of the two bones Fig. 360). 

Synovial Membrane.— The synovial membrane of this joint is part of the great tarsal synovial 
membrane (Fig. 360). 

Movements.— The movements pel-mitted betvsreen the navicular and cuboid bones are limited 
to a shght gliding upon each other. 



Deltoid 
ligament 



'/M^J^' Talofibular 
^^"^^^ .^k ligament 



j| Tnterosseous 
talocalcaneal 
ligament 




Metatarsals 
Fig. 360. — Oblique section of left intertarsal and tarsometatarsal articulations, showing the synovial cavities. 



Intercuneiform and Cuneocuboid Articulations. — The three cuneiform bones and 
the cuboid are connected together by dorsal, plantar, and interosseous ligaments. 

The Dorsal Ligaments (ligamenta intercuneiformia dorsalia). — The dorsal liga- 
ments consist of three transverse bands: one connects the first with the second 
cuneiform, another the second with the third cuneiform, and another the third 
cuneiform with the cuboid. 

The Plantar Ligaments {ligamenta intercuneiformia plantaria). — The plantar liga- 
ments have a similar arrangement to the dorsal, and are strengthened by slips 
from the tendon of the Tibialis posterior. 

The Interosseous Ligaments {ligamenta intercuneiformia interossea). — The inter- 
osseous ligaments consist of strong transverse fibers which pass between the rough 
non-articular portions of the adjacent surfaces of the bones (Fig. 300). 



358 SYNDESMOLOGY 

Sjmovial Membrane. — The synovial membrane of these joints is part of the great tarsal synovial 
membrane (Fig. 360). 

Movements. — The movements permitted between these bones are limited to a slight gliding 
upon each other. 

VI. Tarsometatarsal Articulations (Articulationes Tarsometatarsese) . 

These are arthrodial joints. The bones entering into their formation are the 
first, second, and third cuneiforms, and the cuboid, which articulate with the bases 
of the metatarsal bones. The first metatarsal bone articulates with the first cunei- 
form; the second is deeply wedged in between the first and third cuneiforms 
articulating by its base with the second cuneiform; the third articulates with the 
third cuneiform; the fourth, with the cuboid and third cuneiform; and the fifth, 
with the cuboid. The bones are connected by dorsal, plantar, and interosseous 
ligaments. 

The Dorsal Ligaments (ligamenta tarsometatarsea dorsalia) . — The dorsal ligaments 
are strong, flat bands. The first metatarsal is joined to the first cuneiform by a 
broad, thin band; the second has three, one from each cuneiform bone; the third 
has one from the third cuneiform; the fourth has one from the third cuneiform 
and one from the cuboid; and the fifth, one from the cuboid (Figs. 354, 355). 

The Plantar Ligaments {ligamenta tarsometatarsea plantaria). — The plantar liga- 
ments consist of longitudinal and oblique bands, disposed with less regularity 
than the dorsal ligaments. Those for the first and second metatarsals are the 
strongest; the second and third metatarsals are joined by oblique bands to the 
first cuneiform; the fourth and fifth metatarsals are connected by a few fibers 
to the cuboid (Fig. 358). 

The Interosseous Ligaments {ligamenta cuneometatarsea interossia). — The inter- 
osseous ligaments are three in number. The first is the strongest, and passes from 
the lateral surface of the first cuneiform to the adjacent angle of the second meta- 
tarsal. The second connects the third cuneiform with the adjacent angle of the 
second metatarsal. The third connects the lateral angle of the third cuneiform 
with the adjacent side of the base of the third metatarsal. 

Sjmovial Membrane (Fig. 360). — The synovial membrane between the first cuneiform and 
the first metatarsal forms a distinct sac. The synovial membrane between the second and third 
cuneiforms behind, and the second and third metatarsal bones in front, is part of the great tarsal 
sjTiovial membrane. Two prolongations are sent forward from it, one between the adjacent sides 
of the second and third, and another between those of the third and fourth metatarsal bones. 
The synovial membrane between the cuboid and the fourth and fifth metatarsal bones forms a 
distinct sac. From it a prolongation is sent forward between the fomlh and fifth metatarsal bones. 

Movements. — The movements permitted between the tarsal and metatarsal bones are hmited 
to shght gliding of the bones upon each other. 

Nerve Supply. — The intertarsal and tarsometatarsal joints are suppUed by the deep peroneal 
nerve. 

Vn. Intermetatarsal Articulations (Articulationes Intermetatarseae) . 

The base of the first metatarsal is not connected with that of the second by any 
ligaments; in this respect the great toe resembles the thumb. 

The bases of the other four metatarsals are connected by the dorsal, plantar, 
and interosseous ligaments. 

The Dorsal Ligaments {ligamenta barium [oss. metatars.] dorsalia) pass transversely 
between the dorsal surfaces of the bases of the adjacent metatarsal bones. 

The Plantar Ligaments {ligamenta basiiim [oss. metatars] plantaria).- — The plantar 
ligaments have a similar arrangement to the dorsal. 

The Literosseous Ligaments {ligamenta barium [oss. metatars.] interossea). — The 
interosseous ligaments consist of strong transverse fibers which connect the rough 
non-articular portions of the adjacent surfaces. 



ARTICULATIONS OF THE DIGITS 359 

Synovial Membranes (Fig. 360).— The synovial membranes between the second and third, 
and the third and fourth metatarsal bones are part of the great tarsal synovial membrane; that 
between the fourth and fifth is a prolongation of the synovial membrane of the cuboideometatarsal 
joint. 

Movements.— The movement permitted between the tarsal ends of the metatarsal bones 
is hmited to a slight gliding of the articular surfaces upon one another. 

The heads of all the metatarsal bones are connected together by the transverse 
metatarsal ligament. 

The Transverse Metatarsal Ligament.— The transverse metatarsal ligament is a 
narrow band which runs across and connects together the heads of all the meta- 
tarsal bones; it is blended anteriorly with the plantar (glenoid) ligaments of the 
metatarsophalangeal articulations. Its plantar surface is concave where the 
Flexor tendons run below it; above it the tendons of the Interossei pass to their 
insertions. It differs from the transverse metacarpal ligament in that it connects 
the metatarsal to the others. 

The Synovial Membranes in the Tarsal and Tarsometatarsal Joints (Fig. 360). — The synovial 

membranes foinul in the articulations of the tarsus and metatarsus are six in number: one for 
the talocalcaneal articulation; a second for the talocalcaneonavicular articulation; a third for 
the calcaneocuboid aiticulation; and a fourth for the cuneonavicular, intercuneiform, and cuneo- 
cuboid articulations, the articulations of the second and third cuneiforms with the bases of the 
second and third metatarsal bones, and the adjacent surfaces of the bases of the second, third, 
and fourth metatarsal bones; a fifth for the first cuneiform with the metatarsal bone of the great 
toe; and a sixth for the articulation of the cuboid with the fourth and fifth metatarsal b